The Challengers being an odd model is certainly creating some logistical challenges (see what I did there), but part of this decision is diplomacy. It is to shame other countries into sending heavy MBT-s too and for most of Europe these will be Leopard 2-s.
How many tanks does the money laundry need? Even the US does not have enough you friggin dolts. There are logistical chains needed. You smooth brains are annoying.