To co-ordinate arrests of dozens of people - maybe hundreds in this case is difficult at best - multiple teams in multiple locations and trying to hit simultaneously in different time zones - it's quite a mess.

Info can easily leak out, it can't very easily be kept under wraps moving teams about all over the place and if one is not taken down or there are delays, it can leak out and there can be attempts to flee, retaliations, news leaked to other suspects etc.

It's not that different to a multi location drug bust, they can easily go wrong.

So in this case - the best way to achieve that is at the fake inauguration - and or even 1-2 days afterwards when everyone thinks they are out of danger.

Hence all the troops in DC. Everyone in one place, clean swoop in one shot.