13. Bumps, "updates" are limited to once per 24 hours.[2]
21. Old bumps should be deleted. [2]
22. Advertising (this includes mining pools, gambling services, exchanges, shops, etc.) in others threads' is no longer allowed, including, but not limited to, in altcoin announcement threads. [8]

An example: a bump button sounds good as a fix for certain very visible problems, but it also codifies a broken system. People would use bots to bump all of their threads constantly, giving "industrial" posters a huge advantage over casual posters. A captcha could maybe help a little, but there are services where you can pay a tiny fee to have captchas solved for you. (Which opens another question: maybe a comparatively tiny fee should be allowed as an alternative to having you solve a captcha.) A better solution would be to replace the concept of traditional bumping with something quite different, with different bumping models for different types of sections. But that requires further thought. If implementing a bump button was free, perhaps it'd be worthwhile to at least do it for now and fix a few minor problems with bumping today. But since it's a clearly-imperfect solution, this isn't even on my miles-long to-do list.