In my layman perspective there's another argument to be made from Soviet perspective.

Dresden was destroyed by the western countries (US et al). While Warsaw was destroyed by Germans.

So "we" fix what the bad Germans broke. But we keep the mess left by the spoiled West as a reminder.

There is another reason. Russians saw rebuilding Warsaw as a way to rebuild Polish national identity after the ravages of WWII and the severe redrawing of the borders. It was a way to make Poles warm up to the Russian rule over the country. In Germany, Russians had no such sophisticated thoughts, they literally raped and pillaged their part of the country and if Germans wanted to protest they'd be reminded that it was Germany who started WWII. Quite honestly, after what Germans did to Poland and the rest of Eastern Europe, there is zero sympathy for what happened to them during WWII or afterwards.

> for what happened to them during

Nazi perpetrators and victims of the rape and pillage "revenge" are generally not the same people. So yes there's sympathy.