About 45 on the 777s were moving up the the front last week. But 90 is too few too late.
Interdiction of locomotives and bridges across the Dnieper River will slowly make it impossible to get heavy weapons and ammo to the front. There is no other way but rail to move efficiently large heavy loads across the geography of Ukraine
The M777s are relatively light (under 5 tons). We often sling them around under helicopters, but they can be road marched around too, or ferried across rivers - anywhere trucks can go.
Easier than moving tanks.