Again, going on the opinions of others (who are in positions such that they should know, but ultimately it's all opinion) a lot of it (by no means all) is about prestige and being seen and respected as a world power again. Which is not just for show; if people respect you as a world power, they are far more likely to do what you want.

Following the collapse of the Soviet Union, Russia was made a number of promises that really weren't kept (for example, about how far NATO would wander into Eastern Europe) and when Russia objected, they were ignored. The very significant modernisation of their military and the recent adventurism is part of that. Nobody is ignoring Russia anymore.

They did play by the rules; it got them side-lined and ignored, promises broken.