There are plenty of Russians who do not support the invasion, why punish them? Especially when they've been loyal users for a long time?

It is no different when a government uses trade sanctions. All citizens are harmed, whether they are patriots, rebels, neutral or ignorant.

It would be much less fair you to try to judge individuals, and it would not be effective if it only affected a few citizens.

Despite any political dispute, which is not belongs here, Grammarly obviously denied Russian users because they are actually Ukrainian company.

Worth to mention that on the other hand there was some betrayals within Ukrainians who sold a heavy weapons (e.g. tank engine) to Russians even after the war started, luckily there are just a few of them.