"why should I have to pay for somebody's midifile of the same song?"

. . . because someone had the time and talent to create that midi file. It didn't just materialize. There are a lot of songs available on the web for free. Probably most of them shouldn't be free because they were illegally posted after someone else bought them.
Most of us use some of these files, but we should be grateful that we can sometimes find a good free one. If we don't want to go to the trouble of creating them ourselves, or at least searching for them and editing them to our satisfaction, then we should be ready to pay someone to do all this work for us. A dollar or so per song actually isn't really that high. You only have to buy it once, but you can use it as often as you like.
I'm being hypocritical because I use a few I've "found" myself.
I suppose it's similar to the problem of "free" MP3s being downloaded by the millions. But that's another can of worms . . .
DonM