That's because Ditto only presents content from it's own relay. It can and does filter on the backend using Nostrify, which can support NIP-13 PoW, but needs WoT implemented still.

https://nostrify.dev/

Otherwise it's up to reporting spam and hoping the operator sets up or improves the policy set.

Some examples: 
https://gitlab.com/soapbox-pub/gleasonator-policy

https://git.sleepingcro.ws/SleepingCrows/ditto-policy
(my personal attempt at combating replyguy, and pruning RSS, & porn bots) nostr.fmt.wiz.biz 

 The problem with ReplyGuy is that he's aware of my policies and actively circumventing them. So I figured out his IP and blocked it, but... Ditto also ingests posts from other relays, and those relays are getting hit by his spam and not blocking it, so it's filtering down to us from there. 

 I'd assume he's using a VPS provider, maybe lodge a complaint there? 

 I'd assume he's using a VPS provider, maybe lodge a complaint there? nostr.fmt.wiz.biz 

 Tis' the cost of anti-censorship i suppose. 

 Tis' the cost of anti-censorship i suppose. nostr.fmt.wiz.biz 

 He didn't happen to be the one coming out with a golang http header  yeah? 

 He didn't happen to be the one coming out with a golang http header  yeah? nostr.fmt.wiz.biz 

 I do recall and still have error logs of an address out of a Contabo VPS that was sending requests to the relay 2-3 times a second 

 I do recall and still have error logs of an address out of a Contabo VPS that was sending requests to the relay 2-3 times a second nostr.fmt.wiz.biz