The reference is to a old action movie called Demolition Man. In the movie there was only one restaurant that survived the franchise wars. In the US it was Taco Bell and in Europe it was Pizza hut.

https://en.wikipedia.org/wiki/Demolition_Man_(film)#Filming

You can also read up on the Three Seashells.

Pepsi sold them off a long time ago.

Yeah the full and complete story of the joke in this comment chain:

In 1993 there was a somewhat offbeat slightly Sci-Fi action movie called Demolition Man starring Sylvester Stallone and Sandra Bullock. Stallone plays a cop from the then future dystopian year of 1996 being frozen for several decades only to emerge into a late 21st century future where the entire world is rated G, the police have to be told what a murder is.

In one humorous aside/extremely blatant product placement, Stallone's character is invited to a fancy dinner at Taco Bell. Making small talk with Bullock's character on the way, he mentions that he feels strange being taken out to a fast food restaurant, and Bullock's character says that Taco Bell "won the franchise wars" and so now ALL restaurants are Taco Bell. Cue the cast arriving at a fancy four-star restaurant that serves plates of artfully drizzled sauce with a futuristic Taco Bell sign out front.

That's the original version that Americans are familiar with, at least. In 1993, there were effectively no Taco Bell restaurants in the UK (There were two; both at RAF bases that had attached USAF presences, and the restaurant was restricted to base personnel) so the joke/product placement was lost on the British public. I don't know if they altered it in theaters (or if the movie got a theatrical release in the UK at all) but for television broadcast in the UK, the scene had its dialog redubbed to change the joke to Pizza Hut, a sibling brand at the time under PepsiCo's fast food division. Which is why you will see people referencing the movie swear the joke was Pizza Hut rather than Taco Bell: Because in their region it was.