The argument to keep building it was they'd already invested billions and it would cost millions of dollars to stop building it.
I guess that cost would have been from contract guarantees to the builders or something.
Looks like when the Soviets stop building something they just walk away.
According to Wikipedia [1] the Buran-program was cancelled when the Soviet Union stopped existing. It was a time of chaos and many parts of the country were not working. Resuming construction on a space shuttle was probably at the very bottom of their priorities in 1990.
The first Buran test flight was on November 15, 1988. Literally the next day (November 16), the Estonian SSR basically declared sovereignty by saying its laws would precede those of the USSR, and the house of cards started collapsing.
It was / is huge. 27KM from memory. It blew over budget, because less relevant, and closed. There is a mini collider that is active in one of its 'corners'.
Today, it's empty, and a little bit flooded. They keep pumps on to keep the water out, but the place is, essentially, ruined.
I'm too young to have been part of the physics community at the time, but talking about the SSC can still elicit winces and melancholy today. I'm sure it was over budget; I suspect that most big government projects are. (I've heard people talking about the SSC say that that was standard: that an expectation of overruns was essentially built into the system on all big projects, from the scientists all the way up to Congress.)
I recall hateful accusations of "mismanagement" that boiled down to supplying liquor at a Christmas party. Drunk physicists... the horror. Oh, and the fact that our contribution to the ISS had roughly the same cost estimate meant... for some reason, that it was prudent to choose between to the two.