Thank you for providing this valuable explanation -- I haven't heard this perspective expressed elsewhere. The fact that old rules would never get deleted but continue to drain resources makes some design decisions make a lot more sense.
One particularly pernicious outcome is that some ad blockers tout their rule set sizes as a feature, and users choose among blockers based on it, when if anything it is probably negatively correlated with blocker quality -- it's not necessarily a sign you're comprehensive so much as that you don't care about efficiency or cleaning up after yourself.
That's of course an oversimplification. But people who believe they're technically knowledgeable and adept are just as likely as other folks to fall for bullshit and be convinced to do things contrary to their own self interests. It's just a different type of bullshit.
No one wants to hear that, because we all want to tell ourselves that maybe everyone else is gullible, but WE'RE smart and rational. To a close approximation, though, none of us are.
Now consider that the extra drain can be practically zero, and you get back to those decisions making less sense