Maybe tentacle monsters are so invasive and domineering is because they're just derpy little things in the middle. So they find people and stuff and cram and drive their appendages into everyone they come across as a way to compensate.
It certainly doesn't do this one's ego any good when its best butt-stuffing assault is not met with the result it was expecting! Guess that's what it gets for stuffing a hungry butt like Uryl's..