Oh man, are you fortunate, because a friend of mine and a great scholar, Paul Musgrave, has written an entire article about this: Mikhail Gorbachev’s Pizza Hut Thanksgiving Miracle, Foreign Policy (2019).

Now, unfortunately, you need subscriber access to read the article. But the basic argument is that yeah, Gorbachev was hard up for cash. Musgrave notes that the end of the USSR was essentially a forced retirement for Gorby, and because of his problems with Yeltsin, he had no cash whatsoever. Yeltsin had audited his foundation and seized the cash, and Gorby's post-Soviet pension was not indexed for inflation, so he was making the equivalent of less than $2 a month.

He could get money from giving lectures, and writing a book, and so on, but he needed a lot of cash, quickly, if he was going to get his new foundation off the ground, and the Russian government and people were not particularly keen on him. You have to remember that while in the West Gorbachev was seen as sort of a liberating, humanistic figure, in the former USSR he was seen as a remnant of the old regime (whose commitments to transparency and freedom were quite limited — remember, he oversaw Chernobyl as well as many other things), and one whose actions had, for better or worse, plunged the country in a very uncertain place. He was not beloved by anyone; the hardline old Communists saw him as having destroyed the nation, and the new non-Communists saw him as an old Communist, hanging around.

Musgrave's article goes into the details of why Pizza Hut was in a place to do this — they were expanding globally, they had a lot of cash, they wanted to improve their perceived prestige and status — and why they saw this as a good opportunity for them. But for Gorbachev, it was about cash. Without cash he wouldn't have a retirement, much less one in which he would be a force in the new world (e.g., as the head of an important foundation).

Gorbachev had a lot of clear uncertainty about the whole thing — it was degrading, obviously, to go from the head of a superpower to shilling for Western pizza. But as Pizza Hut had other options (they were seriously considering Muhammad Ali instead), Gorby finally relented. My favorite part of the article:

Gorbachev finally assented—with conditions. First, he would have final approval over the script. That was acceptable. Second, he would not eat pizza on film. That disappointed Pizza Hut. “We always wanted the hero of the ad to eat the pizza,” Helbing said.

Gorbachev held firm. “‘As the ex-leader, I just would not,’” Helbing recalled Gorbachev saying.

O’Neill Bistrian suggested a compromise: A family member would appear in the spot instead. Gorbachev’s granddaughter Anastasia Virganskaya ended up eating the slice. Pizza Hut accepted.

Now, Gorbachev would publicly justify the commercial on more than crass grounds — he would talk about how it symbolized unity and socializing and all of that — but it was clearly really about the money.

Anyway, the article has a lot more in it than the overview I've given here. Definitely worth tracking down if you want a good read! For what it is worth, Gorbachev denounced Musgrave's article and denied it was as crass as all that... but he would, wouldn't he?