Footballers careers start from a very young age if you want to make it to the very top. You are basically training from the ages 4-16 unpaid for your career. People will say 'they do it for enjoyment at that point' which yes is true but still all that training is necessary to make it as a pro. Plus in the Academies the football is less enjoyable. It's too regimented.
I had to give up playing with my School team as Liverpool blocked me for playing for them in case I got injured. That was from years 7-10 in school. They won the County Cup and had loads of great times playing in tournaments and travelling a way. I then got released and was allowed to play the last year (11) for my school and I loved it, but also felt I missed out on all the other years. I had to travel 30-40 mins to training 3x a week. You have to sacrifice quite a lot that you don't even realise.
Then if you make it as a pro, which is very very tough, you don't get paid much for the first year or two unless you're a Greenwood. At most clubs, you are on a youth contract that pays pennies. Then if you are fortunate to make it pro, but not quite good enough for PL or Championship, an you end up just an average L1/L2 player, you are on anything from £400-£1200 a week. Not bad money if you are the upper end but when you consider this money is going to reduce as you hit 30, whilst in most careers your wage rises as you get older, and stop completely when you hit 35 then it's quite worrying.
For me, if you do manage to make it to the very top level in the PL you deserve the money you get. You pay huge taxes and it goes back into the economy, you get abused with death threats to you and your family, racist abuse, difficult to go out in public without being harrassed sometimes, everything is under the microscopic lens with regards to your public life and you are judged massively. What other job would you turn up to work and have 30,000 people calling you a 'c***' etc. Plus the pressure that comes with playing and the realisation that you career ends at 35 and you have no skills.