1. No games
Say, where can I pick up a version of BF1942 or Doom 3 for Macintosh?
2. no software in general
When things like new P2P apps come out, it's pretty much invariably on Windows or Linux. I have NEVER encountered a cool new program and then said "aww crap, that sucks, it only runs on Mac!"
3. no one uses them
According to
http://www.pcmag.com/article2/0,1759,1745930,00.asp Macs have 2.7% of the market as measured by online usage. That's behind Linux at 3.1%. So yeah, essentially no one uses them.
4. They aren't compatable with PCs
When I make a website I need to see how my pages render in IE since it has ~90% market share. Whoops! Can't do it. Nor can I drop a random Windows CD in and install whatever I want. Sure there are emulators, but they don't have the same performance as a natively-run program.
5. You can't modify them
- Apple maintains a stranglehold on hardware and software (not that this is necessarily a bad thing, since the idea is to ensure consistent & reliable operation) which limits the number of available products.
-They have a very low market share, which means there are less companies interested in supporting them in the first place.
-Among the people who DO buy Macs, a very large amount of them them just want a cute conversation piece.
Those 3 things make it much more difficult and impractical to modify a Mac.
6. They aren't as fast
Sure there are fast Macintoshes, but in most all cases a PC at the same price point will be faster.
7. Difficult to use
This one's too subjective. I'm sure I'd have a hard time finding my way around a Mac for a while, just like a Mac user would be put off by Windows or Linux at first.