It would seem to be the lowest moment in the life of Moshe Rabeinu and yet the Torah prizes it as his crowning achievement. Indeed that is how Rashi understands the climatic closing of the Chumash, the lingering last line of the divine "hesped" accorded to Moshe, (Devarim 34:10-12), "There has never been a prophet who equaled Moshe...who spoke with Hashem with unparalleled clarity who delivered miracles in Mitzrayim...and who received the luchos...and (according to Rashi) who broke the luchos for everyone to see." Why did Rashi see the breaking of the luchos as worthy of being in this appreciation of Moshe altogether, let alone the culminating entry of all of Moshe's accomplishments?
There is much discussion regarding why Moshe broke the luchos. The ohr hachayim tracks two traditions debating whether Moshe acted with divine guidance or acted independently and only afterward received divine appreciation. The Kli Yakar explains that Moshe destroyed all evidence of a spiritual drop and wished to rid the world of anything that could weigh in against us.
The Meshech Chochma finds that now these luchos were no longer infused with dedication to Hashem. Thus keeping them would send the message that there is value in service that is empty of genuine faith and total deference to Hashem's will. This risk justified doing whatever was needed to prevent sending that message.
I was taken by another conjecture. (Unfortunately time constraints did not allow me to search where I saw this insight, but that should not stop us from sharing an idea together.) Perhaps Moshe Rabbeinu is indicating to us that while the Torah is immutable, the style and presentation of Torah teachings often must change from one generation to another in order to be effectively communicated. The style and format that connected with the Jews prior to the chet ha'eigel would no longer be effective after the chet, since our people after the chet would be forever different.
The luchos embodied all that Har Sinai was: Hashem's insistence on joining Klal Yisroel in this world and gifting us a permanent proof of His presence. For Moshe, the luchos represented his personal journey to becoming similar to an angel, his successfully leading the national journey from slavery to revelation, and the like. It takes a Moshe Rabbeinu to set aside his personal investment and embrace that which will speak to the younger and the newer. To recognize that the next generation needs a different "hook" and a different presentation in order to teach the same Torah can be supremely disappointing, but the picture of Moshe Rabbeinu can inspire us onward.