Introduction
The question is based on similarities between wine and bread, contrasting with their differences in blessing style.
Bread is better than wheat seed. So praise for the gift-bread is a bigger than praise for gift-seed. The main reason why humanity grows wheat is for bread to eat. the fruit (i.e. the proceeds from wheat) is the bread.
Sources and explanations
The Mishna in massechet Berachoth, chapter 6, says that on fruits (proceeds) coming from earth, "He says Bore Peri Haadama except for bread". You learn that the bread is considered as the fruit, you learn the definition of the word "fruit". Fruit is the aim of the production. Idem for wine.
So,
the definition of fruit in this topic is not the biologic-botanic definition. If the aim is good it is the fruit.
The wine, for example is considered as the fruit of the vine (step 1
[20]), so the blessing must be "Bore Peri Haets". But wine is a very special fruit of a special species of tree witch fulfil an important function, the vine (step 2
[21])
the tree witch was planted by Noah. But wine is not used as main meal (Gemara 35b
"Suppose a man makes it the basis of his meal. what then? - He replied: When Elijah comes he will tell us whether it can really serve as a basis; at present, at any rate, it is ignored because no man thinks of such a thing.
") Bread is the fruit of the wheat sprouts, and must be "Bore Peri Haadama" (step 1
[10]) but it is more than a fruit of the earth, this is the best aliment, the main aliment. Main aliment is called bread, so, on a loaf, we bless Hamotsi lechem (step 2
[11]). For olives oil the Gemara ask why not Bore Peri Haets or B.P. Hazait or B.P. Ets hazait. But it has a sharp taste and do not deserves this bracha
[30].
Grapes are not better than other fruits, so no need to bless specialy the vine when eating grapes.
Wheat seed is not very pleasant food (eaten raw it is not usual) also when grilled, so no need for calling Chita, just Adama if grilled.
Why do we not mention "fruit"?
Suppose that bread is coming from a fruit of a tree. And this Tree is called Chitim. So, at first sight, you where right. According to the reasoning given for wine (not sure 100%) we might have though to blessing "Bore peri Hachitim". Here is the point of the O.P.
We can perhaps answer that the word "Lechem" is the greatest praise because it is more functional for humanity. (lechem is perhaps originally synonym of subsistence and subsequently the name of some good product of 5 species of cereals[12]). As soon above, an intermediate step before Hamotsi is Mezonot.
CONCLUSION
Bread is more defined as fulfilling a need than as a fruit of a plant.
Notes concerning bread:
[10] It is implicit in Gemara 35b that the seel of wheat is improved by bread making.
[11] The Gemara stated that bread has a satiating effect. A particular attention should be given here to the
two different levels, "Mezonot" and "Motsi". - Mezonot blessing is attributed to the products of the 5 cereales witch satiate,
- Hamotsi for a subcategory: The main component of meals.
[11] A proof that Lechem is the name of a function is for example the case of Kuba DeAr'a, a kind of pancake made from liquid paste (according to some opinions in Tosfot, Rashi, Rashba) backed in the sand. Its blessing is Mezonot, but Mar Zutra made it the basis of his meal and said over it the blessing, 'who bringest forth bread from the earth' (Berachot 38a). According to some opinion in Tosfot, Kreplech too. And it is clearly morphologically distinct from standard bread. So,
"Lechem" is a name of function.
Notes concerning wine
[20] The first argument concerns the fact that the wine making is an improvement of the product of the fruit tree "אישתני לעילויא". Wine is the best product that could be obtained from vine cultivation. Wine is best than grapes. The proof: The majority of vines are planted and grown for production of wine.
Theoretical example: If we obtain wine from Grenada, this wine is SheHakol. If in 10 years we will see that most producers cultivate Grenada for wine, following some Rishonim (Rashba), the wine will be bore peri haets and the botanicly called fruit, Bore Peri Haadama.
[21] The second argument concerns the fact that wine has two special qualities that other fruit don't have. He brings fun and he satiates. So, a common fruit's blessing is not sufficient for it.
Note concerning olive's oil:
[30] The Rambam, Ahava, Berachot, 8, 2
ועל השמן {כוונתו לשמן זית}--הוא מברך בתחילה, בורא פרי העץ {It is recognized that olive oil deserves blessing Bore Peri Haets, but the strong taste of this oil must be attenuated by a "seasoning"} : במה דברים אמורים, שהיה חושש בגרונו ושתה השמן עם מי השלקות וכיוצא בהן {the result of the seasoning is a mixture of water of cooking of chards and a small part of olives oil.When drunk for pleasure by a man with angina, its required blessing is Bore Peri Haets} , שהרי נהנה בשתייתו; אבל אם שתה השמן לבדו, או שלא היה חושש בגרונו--מברך עליו שהכול, שהרי לא נהנה בטעם השמן
The Magen Avraham (See S.A. O.C.
202, 4 )
Afterword
At first glance I thought it would be better to introduce points of Rama Mipano about "Hamotsi Lechem Min Hashamaim" (or mamtir lechem according to others) and to explain the lake of the name "fruit" by the fact that there is no tree (in the sky or bellow ground) in bread production. Indeed, unfortunately, unlike the case of wine-vine couple, bread has no tree. So "by the impossibility" we have to look at the Earth and Sky. But that is a secondary topic. The essential Chidush (and topic of OP) is the lack of the name fruit. It is true for Mezonot too. So it was essential to states that.