Landfills actually seem to be endorsed by civil engineers to some degree (while also acknowledging that genuine Reuse, Recycle, or Combustion of products would be better)

GRADY (Practical Engineering) has videos on this. Here is one

I can't really remember what i learned from this video though - it might be entirely about the effort it takes to protect the surrounding soil from leeching (chemicals and plastic want to go into the soil and mess it up!). So the sole engineering benefit of landfill might be that it literally fills in places where soil was "mined" to be used as gardening and construction materials.

I think it's quite a bit more complicated than this. The concept of disposing of something always existed, but for most of human history that meant just leaving waste where it fell or at most tossing it at the edge of the village.

It's only once larger settlements appeared that a need to concentrate waste in one location to avoid despoiling the entire area became necessary. This was greatly compounded with the invention of manufactured materials that don't biodegrade like glass and plastic. There was no other solution to this than to concentrate and bury waste so it didn't end up everywhere.