Soccer Referee Uniforms

Back in the good old days, when football is played, the referee and linesmen would be dressed in black or red if either team had a dark color. Their clothes have also been very formal and more like uniforms.

Why is it these days, referees and linesmen can dress in clothes of all the colors they like? They also wear T-shirts nowadays, unlike before.

What led to this change?

Sponsorship

Because the world is causal