You ask "Why do professional footballers cheat?" You might also ask ...
Why is the next World Cup in Qatar?
Why did 12 teams try to break away to form a European Super League?
Why do parents on the touchline shout, F and blind as they watch their kids play?
Why did Sepp Blatter receive a twelve year ban following the end of his tenure as President of FIFA?
The answers are all related, in my opinion.