They're a revenue generator. Full stop.
I was the 54th person to be Citrix Certified Enterprise Architect (CCEA) back in the day.
It was a bloody tough cert to get, made even more so by questions on products that were no longer in support.
At the end of it, I got a badge, a certificate that looked like it'd been printed on an original HP DeskJet printer and was on paper so thin you could see right through it.
But delight of delights I got access to a CCEA-only website. Which consisted solely of a list of exams required to become CCEA accredited.
At the same time I was working towards my MCSE in Windows 2000, having passed the Windows NT networking essentials exam.
It didn't take me long to realise that these things exist for one purpose - to generate revenue for the vendor. By making it a pre-requisite to have x numbers of y certifications they guarantee that partners will cough up to have them.
I've been in the position where, at the annual renewal people (including me) were being asked to sit down over a week and take numerous exams to qualify because we were the ones they thought had the better chance of passing. Try getting on a course any time in the year otherwise and you had zero chance.
So my last MCSE was in Windows 2003 and I seem to recall it was a single exam. I am yet to find a scenario where my experience combined with the companies I've contracted to (MS, HP, Siemens, etc etc) in addition to the kind of projects I've been involved in hasn't been enough.
I _have_ been queried on why I never bothered to become, for example, PRINCE2 or TOGAF certified and my answer is always the same: I don't need the certification to be able to converse with a PM and since I am not a PM I don't need PRINCE2 and I would prefer a common sense model that has proven to work.
And traditionally I am shy of hiring someone with multiple certs - particularly from multiple vendors - for one, it shows a general lack of specialisation and two when do they have time to fit their day job in??.