They dont do it because pans across the front soundstage arent as smooth when the tweeters are not at the same height. Placing the CC above the other tweeter heights may reduce the seamless presentation and increase the likelihood of timbre matching/off axis response issues. I'd agree with the first row being priority and the guest row response being easily acclimatized to by guests. The only reason we tweak and obsess over such details in our setups is because we live with them and notice even miniscule optimizations. Your guests may not even notice once they are in front of a huge screen.
My experience is guests are most impressed by LFE and clarity.
