On one hand, if instagram is anything like twitter was before elon got there, they probably employ hundreds of people who should have been able to figure out how to block or censor hashtags like these. Shame on them for not doing so. The probably did a good job of censoring certain political or social topics, like anti vax hashtags for example...?
On the other hand, I don’t know about the internal mechanics of these platforms, but it looks like these headlines and articles are being disingenuous in a way. The ‘algorithms’ simply filter content based on what peoples interests and patterns have set. The algorithms don’t know that they shouldn’t be allowing certain interests unless the programmers and administrators specifically block them, but the article makes it sound like instagram was intentionally promoting these specific topics or themes.
As you say, they should be able to block certain stuff. The fact that they aren’t doing so would be, in a way, promoting it. The CEO’s should be charged with sex crimes against minors if they fail to do something about these things.