There are numerous factors that all came together to result in Russia's current poor tank situation, but here's a few:
(1) Russia spent most of the time since the fall of the USSR bankrupt, as a result of taking on all of the USSR's debt in exchange for being internationally recognised as it's successor state (thus inheriting UN seat/etc). This meant that until the last 10 years they couldn't afford to maintain the tanks they had let alone develop new ones properly. The first post-USSR tank they have unveiled is the T-14 Armata and they currently only have two prototypes. All of their other "new" tanks are 30+ year old Soviet designs with features from the 90s/00s bolted on.
(2) The USSR spent the better part of it's last decade going bankrupt, this means that in that time tank development stalled and was downgraded for budget reasons, the knock on effect being the tank programs Russia inherited were already stalled/slowing compared to western development. In example, they had three tank families, the T-64 (high end tried and tested design that was never exported), the T-72 (cheaper/weaker alternative to the T-64 that was designed for export and to boost the USSRs tank numbers) and the T-80 (based on the T-64, advanced tank designed to replace the T-64 as the USSR's top tank).
However, due to the aforementioned imminent bankruptcy of the USSR they decided to end development of the T-64/T-80 and focus entirely on the T-72 as that was the cheapest option. This is the program Russia inherited and why they had no choice but to continue the development of just the T-72 for a long time, this resulted in the T-72BU, which Russia renamed the T-90 in the early nineties in order to try and hide the fact their best tank of the 90s/00s was actually a design from the 70's and the USSRs third best tank.
(3) Because Ukraine was now a separate country and that was where the USSR's best tanks were designed/built, this meant that Russia no longer had access to the T-64 factory so couldn't get parts effectively, this meant they had no choice but to sell/scrap most of their T-64 tanks despite them being superior to the stock of T-72 they inherited (many of which they are now using in Ukraine).
In addition the diesel engine T-80UD tanks were all produced in Ukraine so Russia can no longer maintain/replace the engines in these tanks (many of which have been cannibalised so their improved turrets can be placed on older T-80s). This is a problem as the standard version of the T-80 which they use was designed for defence not offence, and so while it's repurposed helicopter engine is great for operating at down to -40 while defending Russia against a NATO invasion it's terrible for actually invading anywhere due to dismal fuel consumption.
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So basically, Russia only really has at it's disposal:
- Old Soviet T-72 tanks that have been poorly maintained.
- Old Soviet T-72 tanks with newer bits bolted on that have also been poorly maintained.
- Old Soviet T-80 tanks that have been poorly maintained and are really not designed for invading anywhere but they have to be used in order to beef up the numbers.
- Some updated T-72 tanks built in the 90s/00s with a T-90 label taped on (which already had their flaws exposed by Syrian rebels with improvised weapons).
So there you have it, hope the explanation wasn't too long.
