Basically unless you're already making a living by the accumulation of a lot of that kind of $800 transaction, the hassle involved in accepting just one of them as a one-off makes it not worthwhile (tax questions, potential conflict of interest with existing employer, dealing with people as paying clients rather than as people one can simply say 'no' to, etc...) And there's a massive chasm between "maybe once in six months somebody offers you $800" and "enough money coming in to quit the day job".
However, the more common scenario when consulting -- and I'm sure many are nervous about this type of play-out -- is the client drags the deal on and on and on...and argues about the price...and pays late...and has endless change requests...and is surpirse that ECRs cost money...and needs just one more meeting about $THING..and...and...and.
I've always assumed that's why we've been rejected...how can someone tell we're NOT LIKE 90% of the consulting buyers and mostly know what we're doing and have a straight-forward deal?
Were they administratively prepared to accept payments? For instance, did they have business bank accounts, invoicing, tax numbers, record keeping - if not, then it would be a hassle to do all that in order to receive a once-off payment for a days work, even if the rate is generous. Indeed, they'd need to "go commercial" to make the hassle worthwhile. So it may not be as cut-and-dry as you thought.
I've had multiple experience trying to pay FOSS developers where they wouldn't even accept a donation.
The rationale seems to be that they don't want the increased responsibility that comes with offering a paid service.
This is a really big deal. There's a step change in responsibility that happens from "offering free project you do whatever" to "you're paying me for a service." Even if that service is just consulting, it's still a big difference in responsibility. When it's free you can always walk away whenever you want, even if you were just in the middle of fixing something up.
Besides, in my case at least, I spend so much time working on Redux stuff as it is that money really couldn't even make me do more than I already do anyway :) The only thing I can think of that would qualify would be getting paid a full salary to do maintenance full-time, and I don't want that either. I like building other stuff for the day job, and Redux stuff in my free time.
It is a bit of a pickle, either go full consulting on your FOSS product (which might not be realistic), or work in something unrelated for someone else, getting something in between is hard.
As an open source maintainer I would much rather you pay me than pay your own developer - because no matter how talented they are, if they're doing the work I'll need to spend a huge amount of my time discussing the work with them, reviewing their code and generally being a now-unpaid engineering manager to help shepherd their efforts!
The ideal goal would be to have someone on my own staff who understands and can improve the project's codebase, with your blessing, and who contributes towards the resilience of your project by way of adding numbers (and I'd be happy if they respond to Q&A, within reason, as part of your community, because it's part of my business' dependencies).
For folks in our industry that are not using our software (they are using of the closed-source competitors) we are able to show alternatives and still have conversations with operations folks about methods, ideas and other non-technical methods for businesss-process-automation.
We've also got a segment of customers, they are paying us maintainers to basically do the install and a crash-course for the in-house development teams.
We've even been able to work with some groups who "just wanted to prototype some ideas around our platform" -- which sounded like custom-development right? So, naturally we just bill for the time -- like regular old consulting business. Because our core offering is FOSS we've had a few folks push back "I thought the software was free". Oh it is...however, our time spent with you at your behest is not.
Oddly, I've found some other FOSS projects that I wanted to get some help with -- and led with "I'll pay you to pair-program with me for like four hours and answer my dumb questions" -- I was surprised to be turned down: "we don't want to make this commercial, just file a bug" -- do you want a new bug or do you want $800?
Sometimes it's tough to get folk to understand that our FOSS thing needs money to survive and that free-software is not the same as free-consulting. And another side is that some FOSS folk are actively pushing money away.