Interestingly, I've mostly seen this happen in the other direction - with successfully growing companies.
Weekly lunch for a whole company isn't a huge deal at a startup, and it's not going to shorten the runway much. But when you've suddenly got 10x or 100x the original employee count it starts to look less pleasant. By the time a company is spending several salaries worth of money on free lunches, it probably looks tempting to cut them. (And it's probably less destructive when everyone knows the finances are going strong.)
I work in a division of my company that was acquired by it 10 years ago (about a year or 2 before I started working here). When I started, there was "pizza Friday" every week. About a year later, it was every month (and headcount was much higher). A year later, we were building out into another part of the building that we took over when the previous tenant's lease came up. Fast forward. Now, 2/3 of the office it gone, offshored. There's a monthly bagel Wednesday. I've only stayed this long because my manager is pretty awesome.
But I feel like I've seen both sides: Growing out of childhood and falling into senescence. The next time I see this pattern, I'll leave a couple years earlier.
Early-stage startups have real trouble attracting talent. The more the business grows, the less desperate recruitment becomes. Cutting on perks is a decent signal of this: people have actually heard of the company, the stock options seem to really have value, etc, so there's no need to bribe workers with unlimited everything.
Weekly lunch for a whole company isn't a huge deal at a startup, and it's not going to shorten the runway much. But when you've suddenly got 10x or 100x the original employee count it starts to look less pleasant. By the time a company is spending several salaries worth of money on free lunches, it probably looks tempting to cut them. (And it's probably less destructive when everyone knows the finances are going strong.)