Part of it is the flooded market, changes in what my long time clients are making, when they get into any kind of financial crunch they drop photography, or cut their budgets to the point where they don't want to pay me to shoot, but look for some local photographer that is willing to shoot for very little. What they don't do is even offer the shoot to me and allow me to negotiate lower fees for them, I can always piggyback other clients on top of most shoots that will work for everyone. The demand for good sports images is still there, but clients are expecting the same quality from inexperienced photographers, so they accept less and justify it by the budget bottom line, with one of those "It's the best we could afford, so it will have to do" mentality. I had one client that dropped me 3 years ago and have been using a couple of amateurs for all their pictures, thing is that they are still using the pictures I shot for them 3 years ago.
The other side and this may not come out right. I've done so much in my career, that I am running out of assignments that really excite me anymore, it is a bit of a burnout factor. I have had the opportunity to shoot most sports photographers bucket lists several times over. I have always felt really fortunate to have had the opportunities to shoot what I have. I still look forward to every shoot that is presented to me, and the work I produce is still at the level that I have personally come to expect of myself. When I get to the point where I can't deliver consistent high quality images from every assignment I will know it's time to walk away.