What difference does it even make if a large number of the accounts are fake on any social media platform?

The algorithms are based on the level of engagement, so if the fake profiles are able to coordinate, and they usually are, then they can skew the algorithms and artificially promote or restrict the type of content that the masses end up seeing.

It's why so many countries, companies, and political organizations employ fake accounts in order to alter public perception of whatever suits their agenda

It matters in the way any site is used and how effective are the options a site has.

For instance blocking is pointless if you can just make another account to get around being blocked.

Yet blocking is also pointless in another way on this site.

So basically just the option of blocking is pointless. It really doesn't work.

That is one of the effects of multiple accounts on this site options.

It rather depends if the accounts are monetized. If you get paid per account and 1/2 of the accounts are bots or fake you are committing fraud against the advertisers.

It matters to advertisers, because they want to make sure that the impressions they got on their ads are unique individuals and not duplicates or bots.

Even more so. If I have 20 or 30 fake accounts all posting the same believable lie, it makes it look like it's a popular opinion. That sort of thing persuades the easily persuaded into having the same opinion.