here they follow the police of only keep contend without an official publication as soon one is release the content is remove I believe is to keep the health of the site and safety against the attack from copyright infringement, which is a big issue that can cause many problems to the site in the future, as many had seen this has cause many sites to ether have problems in performance of they has just stop working and disappear completely .
Goblin slayer and goblin slayer:year one have official publications with physical copies and digital copies available in multiple places can look in to amazon for example for the English version in the us with it's respective copyrights that forbid illegal distribution of the material in any way or form in that language.
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=golbin+slayer&rh=i%3Aaps%2Ck%3Agolbin+slayer
https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=golbin+slayer+year+one&rh=i%3Aaps%2Ck%3Agolbin+slayer+year+one
an as most scanlator place the message of "support the author ones an official release is available" or "for fans to fans while a official release is available" here they follow suit with that moto or at lease is my way to see it.
here is to the sites rules: https://mangadex.org/rules