There are no warehouse full with weapons in Western Europe. Most of them have been sold. So you would have to take weapons from soldiers, which obviously weakens the military. That is especially true since they have to train.
Then soldiers are needed for tasks, which have nothing to do with Russia. For example the issues in the Red Sea right now. But there are also troops fighting terrorism in a lot of different countries, UN missions all across the globe and so forth. Those are also needed for national security.
Then you have Western troops depolyed near the Russian border. You have Baltic Air Policing and NATO Enhanced Forward Presence, which both are meant to protect the Baltic countries for example. There are quite a few examples like that.
Also it is obviously a problem, when you do not have soldiers deployed at home as well. Russia has things like landing ships and planes.
They are propably out of the high quality ones and the old stuff they have shorter ranges. So they move them closer to the front. Also they are attacking, so they need to be closer due to that.