The price starts to go up steeply once you hit the % of monthly spend.
I'd guess they don't get many resource intensive support queries from the < $10k a month customers (and at that level you probably don't get the A team support)
I work for a retail app and can usually tell when we have or haven't been spending on FB ads when I check our usage numbers for the week.
They do work but like anything it's about choosing the right tool (platform) for the job. We wouldn't run ads on LinkedIn and B2B SAAS companies shouldn't advertise on FB/Instagram.
One of the most valuable things I've seen is that the users on UKPersonalFinance are also not afraid to tell people when they're doing (or planning to do) a stupid thing.
On the flip side of that, you'll generally get a good response if you are planning to do a stupid (within reason) thing but have yourself sorted out, followed the flowchart, got your emergency fund sorted and are paying off your dept.
It's a good place for balance between getting yourself financially stable and enjoying the money you have.
I recently got ambushed with one of these types of interviews. I was going for a senior dev role, in the same industry I've been working on for the last 5+ years.
Had done the normal initial phone interview (overview of experience etc), a take home code challenge (only took ~1hr) then I was asked to come in for a final interview that was to be a 15-20min presentation on project I'd worked on (that related to what I would be doing at the new role) then 15-20min of questions on that project and the technical challenges/solutions.
All this sounded great until I got an email the day before informing me the presentation and follow up questions would be ~20 mins total and then there would be a 20 minute whiteboard session on data structures and algorithms.
I'd guess they don't get many resource intensive support queries from the < $10k a month customers (and at that level you probably don't get the A team support)