The basic answer is that the production lines are already set up for that size. Some number cruncher figured out they would save $0.01+ by not taking the time to switch the production lines from one to another and, instead, just switching the labels.

I bought the bottle of 360 pills at Walmart a couple years ago. Finally ran out and got more. Same brand. Same price.

Suddenly there’s only 200 pills in the bottle AND it’s in a larger bottle now? wtf?

They could have made the pills larger, to fill up the bottle. Then you wouldn't even guess there was something to complain about.

Bottles are made in standard sizes by the millions, they used whatever worked for this product, base on what others here have said.

Pills are mostly filler anyway, just to make them big enough to handle, and also to improve dosing per pill. The active ingredient is usually a very small part of the volume.

I guarantee, if it were cheaper, all things considered, to use a smaller bottle, they would have.

Bigger packaging takes up more space on the shelf, and you can print more branding on it.

The most obvious answer is shrinkflation. They may have sold units with more pills in them before but economic pressures put them in a pickle: increase price for all or keep price the same and reduce content. It's possible they had ordered a gazillion of these pill bottles and have them in storage now. They gotta use them. It would be economically and environmentally mad if they put a million of these bottles in a landfill and ordered smaller replacements.

https://www.mouseprint.org/2013/08/05/the-little-secret-inside-that-big-pill-bottle/

Was it an Amazon owned company?

Weird kinder surprise

My brother hates the pharmacy I use because they to often seem to be out of smaller containers and put things in ones way larger than needed for the prescription.