They sorely despise their femininity, and can only find it in themselves to tie a price tag to it, looking down on the people that patronize their vacuity with time and money. They're in the same phylum as prostitutes, whose assets are readily depreciating with no means to augment them. These are not financially independent people.
They ensnare lonely men and trap them in parasocial relationships that are precluded from being fulfilling. They cannot take responsibility for these men, by design. The relationship relies not on reciprocated devotion, but on the perpetuation of a delusion of a relationship. The men are never better off, outside of never having started, because they're putting emotional energy and resources into someone who could have never cared about them the way they want, and in fact does not.
This isn't merely women meeting a demand. This is women deliberately exploiting the circumstance of lonely (and usually not mentally well-to-do) men, and then bragging about the money they've made by festering social malfunction. It's comparable to you making money off the mentally disabled by playing chess against them. This isn't a complicated chicken-or-egg situation: men can't make women thousands of miles away from them emotionally prostitute themselves. Without the e-thot, the man keeps his money in his fist and has that much less deleterious outlets into which he can throw it.
Actual prostitution requires effort to seek out and has a real community stigma, on top of being explicitly and viscerally loveless given its tactile reality-- a woman, likely with at least two STDs, is renting out her body like a self-warming masturbation sleeve while her pimp (who will beat her black and blue if she doesn't meet her quota) is waiting outside in case he needs to "protect his merchandise". Sinking yourself into waifu culture is about as bad for a man, but the subjects of affection aren't even real people-- you have to be further "down" to even manage immersing yourself in that. The delusion the e-thot provides is much more accessible and free of the grime of reality.
I reckon that this (aside from seeing that they despise their femininity, I don't think much anyone realizes or cares) is at the heart of the hatred for e-thots-- not some weird presumption of jealousy that assumes that men just want to make easy money, even if it means debasing themselves. I don't get the sense that this is readily articulated. Part of it must be because most within internet "communities" don't think for themselves, but instead ape the rationales of those who do without adopting them and making them their own-- pure or adapted to personal taste. There may be a second group who are independently aware of their ire, but are unable to articulate it either because they haven't devoted the time and energy to do so, or because are unequipped/untrained to intently examine their own emotions and desires.
Lastly: I can roundly censure the man who chooses such an obvious delusion, but that's the other side of this coin. People who jump to that when given this kind of prompt ought to plainly say that they don't think women have agency-- or value that isn't attached to their body-- and can't help but to exploit men. The only thing that argumentation accomplishes is casting women as no more accountable than children when we don't even have any social structures where a man takes responsibility for them.