"I've noticed that these horses have run pretty much the same race for most of their pp"
If it ain't broke, don't fix it!
Horses are like people. They are usually better at certain things than they are at others. If you have a horse who excels at 6F you look at 6F races to run him in.
However, and this would kind of point toward your second question, sometimes you enter a horse in a race you know he probably has no chance to win because you want him to quicken his pace, or stretch him out so as to help him learn how to rate better, etc. Sometimes you run him in a race with turns so he proves to change leads in competition. IOW it's more a training exercise than a race they're pointing to, except there's a chance they can get paid for it.
I know a lot of the guys have moved many horses south for the winter meets in Fl,La, and Ca. Add to that the current problem with equine ailments in the NE and maybe there is a shortage for entries, so guys are entering horses in race conditions they might not otherwise in hopes of picking up an easy check.