Well...

First, I just can't seem to shoot them as well as other bows.
2nd, The grip is the worst in the industry -- has been for years and they don't change it.
3rd, they are all with high let-off and I don't like any more than 65%
4th, they don't balance for me well -- may have to do with the grip.
5th, poor tolerences, especially in limb cup to riser.
6th, cams that eat cables -- seems all the 'copy' bows fixed it, why don't they?
7th, they are overpriced in my area -- apparently in Oklahoma they are fairly priced (about $200 less than here).
8th, they have harsh draw cycles (except the Icon which is smoother), Legacy is very harsh on the draw.
9th, lose too much performance if you have to adjust the cam for and 'in-between' draw length.

The first time I saw a Mathews, I wasn't hip to the buzz about them. I picked it up and I thought it was 'cheap' but then I turned over the price tag and got shocked. Then I started to read the ads and magazines and found out they were great...haha.

When I look at the bow carefully, nothing jumps out and yells 'quality' to me.

All the stuff others have said about the advertizing (false claims and such), and the attitude of a lot of yahoos who tell you that your bow sucks because it is not a Mathews rings true. This goes for some dealers as well!

Enough for now -- you asked for honest opinions of why I don't buy them. Many others do and they are good bows (but nothing separates
them from the other brands, IMO). A little refinement and I might give one a shot.