Why 1 Ruble 1965-1985 Is So Expensive

One word: demand. For the past decade or so, the demand on Russian coins (also the prices) sky-rocketed, especially mint sets and uncirculated pieces of particular scarcer dates.
Surprisingly, back in the days you could buy many of these coins for near face value (for instance last month I saw a 1972 USSR mint set with remaining original price tag of 2.20 Roubles on it, and today this set sells for at least 300 dollars).
There are too many varieties of USSR coins, not listed in Krause, so if you are interested, I would advise you to get Fedorin's catalog.

I didn't read the topic properly. I guess this applies for non commemorative 1 ruble coins from 1965 to 1985.

Many of the Soviet coin mintages were never publicly released except for the commemorative coins. As of why - who knows. Some speculated that it could hide how bad inflation was back then. Even current coinage figures remain to be unknown.

I suspect that there were enough coins issued from 1961 to 1967 and this includes the 1967 commemorative coins. From 1967 onwards up to 1975, mintage drastically dropped in particular 1970 to 1973 is known for several key dates, 1970 being the key for 5, 15, 20, 50 and 1 ruble coins. Bear in mind that there were many commemorative coins being issued hence the mintage for normal 1 ruble coins may have been affected.

I find it strange that the commemorative ruble and regular coins were struck in different planchets. That said, Russia still continues to do with the current 10 ruble coins...

I had always assumed the Soviets, as a general extension of their anti-sentimental policy toward history and culture, had just frozen the dates on their coins.

The US did it too--we were still making 1964 dated coins in 1966 to try to hide the level of hoarding that was going on.