Because the compromised Core devs allowed them. Also its funny how Monero shitcoiners support Core devs.
Discussion
the consensus rules allowed them. the rules that luke insisted on changing in 2017
The lack of filters allowed them, retard.
Check again my previous note and also answer yourself why would spammers be worried about policy filters.
you can't make everyone on the planet run mempool filters and even if they do they can be bypassed by telling a transaction to a miner. the consensus rules allow it