Only sinks that would be benefitial are sinks from active marketers' accounts. Those, obviously, would never happen.

Market doesn't get any better when you remove TC or items from dead accounts - they aren't in circulation and thus don't have any effects on it.

Also items can be killed - we just don't do it because there's no need in it. TC sinking (kinda) has a purpose as Torishop has a global TC limit - and even though it gets updated every time we hit the limit, TSAs sometimes sink TC obtained through namechanges and similar sinks. However, there's no limit on number of items in existence - that's why they're usually just sent to some system accounts instead.