Why?  I've found it hard to convince people that full nodes offer additional security. (Indeed, I've found it hard to convince people that SPV clients provide more security than JS web wallets).

Doubly so because the inflationary threat running full nodes is most uniquely suited to fighting is generally not that relevant to businesses. We do not see businesses standing up to fight fiat inflation. Generally businesses care more about differential advantages with their competition, can avoid fixing contract prices in inflation resistant terms, and can afford the resources to invest away (self or otherwise) inflation risks.

In some ways I'd expect businesses to prefer running SPV nodes that get blocks from a single source which cryptographically signs them. The security model is more traditional and thus easier to understand, it completely closes some kinds of risks, and gives them someone to sue if things go wrong (except when the wrongness is produced by a state level threat, but see above). Today we see businesses very frequently depending on parties like bitpay for their whole transaction processing needs, a step even further towards centralization end of the spectrum then SPV with signed blocks.

Decentralization is hard and it's costly. Anyone who believe it will be easily retained in Bitcoin if Bitcoin grows is fooling themselves.