Why is "titkabel" not in Kaddish Yatom?

Question

According to this write up of the development of the various forms of Kaddish, the Kaddish began in Second Temple times as what we now call the "half-Kaddish." Then a section was added for the Rabbis (kaddish Derobonon) and later,

By Talmudic times, it became customary to conclude the prayer service with the Kaddish. A sentence was added (the line beginning titkabel, "let be accepted") that replaces the passage for the rabbis and disciples and asks God to accept all prayers that were recited. This Kaddish is called Kaddish Shalem (Whole or Full Kaddish) and is still said by the chazzan at the end of the service. The full Kaddish includes two sentences, added to the Half Kaddish around the eighth century, that reflect the traditional yearning for peace (Yehei shlomo rabba and Oseh shalom).

Later there is record of the Orphan's Kaddish:

The first mention of mourners saying Kaddish at the end of the service is in a thirteenth century halakhic writing called the Or Zarua. The Kaddish at the end of the service became designated as Kaddish Yatom or Mourner's Kaddish (literally, "Orphan's Kaddish").

In the creation of this form, a line is removed -- the line beginning Titkabel.

What is it about this line that makes it inappropriate for the Orphan's Kaddish? Was the removal simply to differentiate the two forms?

Related.

Answer 1

See here

Citing from סדר טרוייש סימן ב:

After I explained that Tiskabel closes out Shemona Esrei, you now understand why the Kaddish recited by a child does not contain the line of Tiskabel and neither does the Kaddish that follows the recital of Megilos Shir Ha’AShirim, Rus, Koheles and why it is not included after reciting Tzidduk Ha’Din at a funeral and not after a lecture and not in any instance that is not the completion of Shemona Esrei. However, after reciting Selichos which are like Shemona Esrei we do recite Kaddish with the line of Tiskabel. There are those who do not consider Selichos to be the equivalent of Shemona Esrei so they do not recite Tiskabel after completing selichos. Concerning reciting Tiskabel before Selichos, everyone agrees that it is inappropriate to to do so. Not even regular Kaddish should be said unless you recited some verses because Kaddish was composed to be recited after verses as I explained.

There are other related items in this article, esp. some analysis from Ramba"m regarding whether this type of Kaddish is even considered a tefillah and how Kaddish Yatom was formed. Essentially, Kaddish Yatom seems to have formed from Kaddish Shalem and "Titkabel" was eliminated for the mourner, not the other way around (i.e. Titkabel was eliminated, not added.)