They can only make Pride events as huge as they have grown over the past decade or so because of massive corporate sponsorship.
Now that the corporates are starting to realise that the sentiment behind Pride has shifted its focus and that this has become a politically contentious issue with potential for backlash, criticism and much higher reputational risk than before, it's obviously a far less appealing cause to support.
Banks, professional services firms and corporates jumped on Pride to repair their reputations after the financial crisis of 2008, and in the years that followed, Pride was an absolute no-brainer for throwing huge amounts of money at a pretty mainstream cause which made them look all soft and cuddly in attempt to change people's perception of the evil financial industry that screwed everyone over.
And Pride was such an incredibly easy win for the banks and corporates as it requires zero effort on the part of management or HR, as the gay man heading up each corporate's LGBT employee network typically liaises with the Pride committees, rallies employees and organises the whole campaign as long as someone in senior management picks up the cheque for all the printing, the buses, the t-shirts, the drinks, the after parties, and so on.
But now, Pride has served its purpose in restoring the image of banking (as far as it was ever going to, anyway) so it is less necessary to continue to allocate that level of CSR budget to Pride, plus the reputational risk and all the fraught internal meetings it necessitates nowadays means it's simply not worth the risk and hassle when they can chuck their money at causes that no-one objects to, like underprivileged kids or whatever.
Plus, as much as banks want to be seen to support LGBT issues, their HR, PR and CSR departments are usually largely staffed by women (because non fee-earning roles are more parent-friendly) who are often mindful of the industry being perceived as an old boys' club. These departments will have likely encountered employee issues and objections to genderbread man-style training and unisex toilets, etc, by now, so even where many individuals may still be captured themselves, they are nevertheless becoming acutely aware of the growing debate around the intersection of women's rights and transactivism, and they recognise that the risk of being publicly accused of trampling women's rights isn't a great look for an old boys' club either.
Less corporate investment = scaled down Pride events.
Hopefully LGB and T events will just revert to being more disparate and grassroots again anyway - that's how it always was before and how causes can stay true to their own messages. No good was ever going to come of selling out to banks like that, IMO. (Although as a gay person, I can attest to the fact that no-one loves an extravagant piss-up on someone else's dime more than the gays, so I can see how tempting the banks' offer was...).