Hundreds of tanks would require thousands more tank crewmen and support personnel, plus additional vehicle recovery vehicles and teams, plus more mechanics, armourers, radio techs, tons of and millions of $ worth of spare parts and the transport to bring them to where they are needed ( all of which will be new as such will not exist in Ukraine ), etc. Also, different tanks and heavy weapons require training the people to use them. Its not the movies where such trained personnel magically appear and jump in and go to war.
It's never as simple as some would wish.