Why does Moses give `Tochecha` to people who did not sin

Question

Acording to Rashi (and the sifrei, onklos and probably much more mefarshim), the first few psukim(1-4) do not describe a place as the Pshat suggests:

אֵ֣לֶּה הַדְּבָרִ֗ים אֲשֶׁ֨ר דִּבֶּ֤ר מֹשֶׁה֙ אֶל־כָּל־יִשְׂרָאֵ֔ל בְּעֵ֖בֶר הַיַּרְדֵּ֑ן בַּמִּדְבָּ֡ר בָּֽעֲרָבָה֩ מ֨וֹל ס֜וּף בֵּֽין־פָּארָ֧ן וּבֵֽין־תֹּ֛פֶל וְלָבָ֥ן וַחֲצֵרֹ֖ת וְדִ֥י זָהָֽב׃ ב אַחַ֨ד עָשָׂ֥ר יוֹם֙ מֵֽחֹרֵ֔ב דֶּ֖רֶךְ הַר־שֵׂעִ֑יר עַ֖ד קָדֵ֥שׁ בַּרְנֵֽעַ׃ ג וַיְהִי֙ בְּאַרְבָּעִ֣ים שָׁנָ֔ה בְּעַשְׁתֵּֽי־עָשָׂ֥ר חֹ֖דֶשׁ בְּאֶחָ֣ד לַחֹ֑דֶשׁ דִּבֶּ֤ר מֹשֶׁה֙ אֶל־בְּנֵ֣י יִשְׂרָאֵ֔ל כְּ֠כֹל אֲשֶׁ֨ר צִוָּ֧ה יְהוָ֛ה אֹת֖וֹ אֲלֵהֶֽם׃

According to the commentary these psukim are hints made by Mosses to transgressions done the people of Israel:

אלה הדברים THESE ARE THE WORDS — Because these are words of reproof and he is enumerating here all the places where they provoked God to anger, therefore he suppresses all mention of the matters in which they sinned and refers to them only by a mere allusion contained in the names of these places out of regard for Israel (cf. Sifrei Devarim 1:1; Onkelos and Targum Jonathan).

But in Pasuk 3 it is written that this is done in the fortieth year since leaving Egypt just before the entrance to Israel, this means that all the sinners are dead that is the reason they traveled for forty years.
my question is double:
1. what forced Rashi to explain the Torah this way?
2. how does one settle the question on rashi's Parshanut

Answer 1

I think parts of this this M.Y. answer by user6591 should explain things:

The Darash Moshe answers your question. He says the generation that did these sins had already died out. The people he was talking to were their children. He was warning them that they too had the capability to perpetrate these sins and hadn't worked on themselves to rid themselves of the disgusting traits that lead to those sins. This type of rebuke is not fit to say outright, being that they hadn't sinned yet.

Adding to this, one should note that since he was talking to that generation's children, part of that group included those who were below age 20 at the time of the spy mission. That group was not decreed to die in the desert. Thus, Moshe was also directly addressing them, who, probably, did commit various sins, including believing the 10 spies' report, among other sins.

Answer 2

Rav Hirsch says אֵ֣לֶּה הַדְּבָרִ֗ים refers to the entire sefer devarim and is about the lessons that he is attempting to leave with the people who are about to be left on their own.

He was about to depart from their midst and they would have to carry out their task in taking possession of the land without his guidance.

Rav Hirsch says that given the Sifri, they actually gave these names to places immediately around the camp, in order to drive home the lessons that they had learned over the past forty years. As the saying goes: those who do not learn from history are doomed to repeat it. This way, when they return to this place, they can be reminded of the lessons that Moshe Rabbeinu had taught them.

... then it is not impossible that Moses and the people gave these names to certain places round about the plain where Moses used the last weeks of his life to make instructive and admonishing addresses to the people. These names, testifying to national lapses, by bringing to mind these errors of the past were to awaken firm resolutions for a purer, more loyal future.

Answer 3

The Siftei Hakhamim (Deut. 1:1:1) explains that the Midrash seems to be based on the Midrashic interpretation of the root דבר as referring to criticism. Rashi himself references this idea in his commentary to Ecclesiastes (1:1), and gives Deuteronomy (1:1) as an example.

כל מקום שנאמר דברי אינו אלא דברי תוכחות, (דברים א) אלה הדברים אשר דבר משה

Every place where "divrei" is stated, it is naught but criticism, [for example] These are the words "devarim" that Moses spoke.

Regarding whether this literally means that this is the intent everywhere this term is used, see this discussion of such Midrashic statements.