Because professionals are used to train much harder / faster/ sophisticated. Its like to decide go mountaneering with an experienced alpinist. If he decides the route at his level you are fucked but it is his tour.
So if the newbies asked TJ to go light and he didnt well thats fucked, but I guess more in the way of just change training partners and he goes through his routine.
Thats why you have training groups with different skill level. If you go to the pros /experienced as a beginner or dont ask they go easy it really is your fault.
You get caught by kicks & punches that the other ones just slip and soften by head movement.
Practice wrestling / Judo with a beginner and put him to the experienced fighters. He will pretty certain leave the training injured without that being anyones fault than the beginners or head coach to let it happen.
And what I did not mention are the macho beginners with no or TMA background..etc who want to show how its done by attacking full force in the first sparring to go home and tell how they fucked up an mma fighter /pro.. Every gym gets them from time to time.They dont come to train but prove a point. In general they quit because of the hard training and if they try to injure they get a beatdown.