It's not that.
It appears your definition of professionalism has a gray area and margin for error.
If you're winning 9-0 in the 7th inning, and stealing bases it's like you're trying to win the game when you pretty much already have the game in hand. Never kick a man when he's down, and if you're beating a team by that margin of a score, why try to make it worse? If they want to throw fastballs over the plate and you hit homeruns that's one thing, but stealing bases is a strategic move to try and win a close game.
Professionalism and sportsmanship go hand in hand. Showmanship/showing off is not part of professionalism. Want to know why many people respected our team and Bobby Cox in the 90's? We played the game the right way, no major personality problems except Rocker who we eventually got rid of because of his problems.
Harper's showmanship after that homerun was proving he lacks sportsmanship. Julio set him straight. Harper not only disrespected Julio, he disrespects the game, which many players find sacred. Strasburg running off the mound prematurely 4 times yesterday was terrible showmanship towards the umpire. You always hear the phrase "He plays the game the right way", that's code for "he understands how to play, and he also understands the rules and unwritten rules, what to do and what not to do."