Emphasis on "plastic is often not". Only PET (#1 on the symbol) can truly be recycled into new material, and usually it's tossed in with other materials and contaminated enough to make that not possible. There is the reusable path, where plastics are remolded into other purposes, but that's not "really" recycling and likely ends there for that form to eventually degrade and be trashed.

So just make more things with PET and recycle better, right? I'm guessing there's limitations on what PET can be used for given its characteristics vs. other plastics, and it is still cheaper to just get new material for new PET rather than recycle. So of course companies are going to go that route.

The interesting thing that I learned not so long ago from the YT channel Climate Town is that people see the triangle symbol with the plastic type number inside and assume it's recyclable, since that's the recycle symbol. But it's not that symbol, it's just designed similar to give that impression.

Glass is a bugger to recycle as even little admixtures of the wrong stuff can spoil the whole batch. Crush it up and it's very useful as aggregate in concrete, though. In the case of glass it's much better to reuse than recycle.

Glas is also heavy meaning it costs more energy to transport, overall PET bottles actually have a quite good environmental and climate record provided they actually get recycled.

Stainless steel is also infinitely recyclable and should be able to be used without liners. Shouldn't even be heavier than aluminium cans as steel and aluminium are ballpark equally strong by weight (aluminium is stiffer though, not necessarily an advantage). PET is probably going to need less energy of all when recycling, though.