Subpixel rendering is effective but it's also a massive pain in the ass to maintain, especially if you want to take full advantage of the GPU. Microsoft has kept it around for much longer but even they are steadily moving away, bits and pieces of the Win11 UI render with greyscale AA regardless of system settings because their newer GUI toolkits don't even attempt to support subpixel fonts.

That said, for something like a text editor where fonts are central the entire application and the worst subpixel edge cases like animation are unlikely to come up, it's maybe not unreasonable to ask them to go the extra mile. It's going to be a sticking point on Windows and Linux for a long time if they don't.