Russia Ukraine war, page-97139

Ukraine had another 4000 soviet era tanks in storage and were upgrading and overhauling and even exporting these.

started the war with 2500 in operational service

Since the maintenance and repair facilities have been under attack much of the tank overhaul and repair work is shifting to Poland

The attacks on electrical infrastructure will hamper the turnaround time given the constrained number of diesel locos and the amount of war materiel needing to be moved to sustain the forces in the field.

Modern western tanks must mean that they have written off too many of their own and are running low. I'd suggest majority of destroyed tanks is via ATGM or artillery so being western isn't really much of a defence.

The reluctance to provide meaningful support i'd say is because NATO might see it as a waste of precious reserves for their own preparedness to throw their good gear away in Ukraine with barely trained rushed deployment. They are running out of the old retired stuff to give away to Ukraine and will give token gifts of good gear as a political support (plays well domestically) but militarily its not sufficient to change the outcome..