Losses are bound to happen in military aviation. I can remember that a few years ago the US lost about one military aircraft a day due to accidents and noone thought that was weird.
There are many possible reasons:
- maintenance deficiencies
- pilot proficiency
- bad luck
In the 1980s the Royal Netherlands Air Force lost a lot of F-5s (about one a month which is a lot given the low numbers we had, about 200 top).
Most flew against powercables during lowflying training in Norway. Initially pilot error was put forward (as it often is, dead men can't complain), but in the end someone woke up and discovered that those cables were not on the stripcharts used by the moving map display.
Just to illustrate a lot of things can cause crashes...