Bykovo is a major overhaul / rework centre. Given that the Russian airlines have on the whole got more airplanes than they know what to do with, many of the Yaks may be just awaiting overhaul... I've seen this system in Russia in the past, where they park airplanes in need of an overhaul, and sort of rotate the ones they operate, overhauling the parked ones only when the next one is needed in service to cover for an active airplane that's just reached the need for overhaul.
When I was at Bykovo, many of the Yaks seemed to be missing engines, rather than being totally derelict. Could be that engines are more of an issue.
In general though, it does seem that Russian airlines sometimes park airplanes that are not that old... Seen a fair few generally tatty looking Tu-204s, IL-86s and even the odd IL-96 laying around Moscow airports missing things like engines.
There are old pilots and there are bold pilots, but there are no old bold pilots