well put it this way.
if im at risk of breaking a leg or being injured which could ruin my career, would you do it for free? im talking about any job not just football?
would you pressure wash the roof tiles on a large 5 bedroom house roof without any harnesses for free?
then why should a footballer (employee) be expected to do the same? players have had their legs broken and other injuries leading to developing further injuries in international matches.
for example, say you hurt your left knee (ACL), you then start to put more weight and pressure on your right knee, after a while something gives and usually ends up with you getting another completely different due to your first one. this is why some player are usually plagued by injury after injury, because 1 can lead to many more.
now would i put my £100,000 a week job at risk for nothing? or something im going to get hardly any benefit from? after weighing up all the pros and cons only then can you make an informed decision. i certainly wouldnt play for free if it meant putting my job at risk for nothing, the reason why i say this is because i injured my knee playing football and can no longer play because i risk my patella popping out. im going to get it fixed privately within the next year or two, nhs were a joke when i went to see them.