For what it's worth, SPF, DKIM and DMARC were developed by largely
different sets of people, who disagreed without each other about what
was acceptable tradeoffs, what was doable and more.

The "they" you
mention act senselessly because it is not one set of people. Patching
up email against spam is a hard problem and you cannot expect wide
agreement about the best tradeoffs.

IMO the right solution to the
problem at hand is to delete dkim signatures during list processing and
to tell dmarc supporters to either have their cake or eat it.

Arnt