I wouldn't have a problem being in a relationship with someone with HIV, but even if his viral load is undetectable, I would still insist on protection for high risk activities.
And of course, that might mean an actual cure is detrimental to the bottom line, which might impact funding for any of these studies.
This also assumes that the only motivation is money, if a researcher came up with a cure for HIV they would become an instantaneous scientific god, immortalised in writing, films, having streets and libraries named after them. They would be a hero. That motivation is pretty powerful for many (not for all of those things, but the be a hero part).
A subset of the population will become resistant to certain classes of drugs, because people do stop taking drugs etc. And gain resistance, then pass that on, but for a specific individual their current regimen should be good for as long as they take it. Realistically people change drugs every so often as better drugs with lies side effects are released, but not because of new resistance development.
Now this did used to be a bit if an issue since people had to take multiple pills at different times a day. Having to do that makes missing doses easier, and then resistance can develop. But these days most people are on a single pill taken once a day that completely eliminates that risk.
You're thinking of this like antibiotics, when it's really not a comparable situation.