This is honestly something I have been asking for for years. As @ashman70 stated, if it's a technical limit that unraid has, then so be it. I can't say that I've ever seen other OS's struggle with this limit, so I'm not sure its a technical limit vs a LT imposed limit. I've also said for years I would have been happy to buy a Pro Plus or Ultra or whatever license to get rid of the limit. While I'm now running 12TB drives, it would have been a hell of a lot cheaper to buy an upgraded license rather than expensive larger drives. I'm not talking hundreds of dollars cheaper, I'm talking thousands of dollars cheaper.
As to not wanting that much data (or drives) being protected by 1 or 2 parity drives, that's just personal preference. I no longer even run parity drives on my array. At $400/drive and having a main and backup server, dual parity on those machines would be a $1,600 expense. If a drive dies, I replace that drive, and copy the missing data from my backups. So if that was a real concern, give us multiple arrays with each array protected by it's own set of parity disks. Cost issue solved, scaling issue solved. We get what we need, LT makes money, everyone wins.