Almost all of the trash that escapes into nature, especially the sea, is caused by a bad trash collection practices. This often happens on fishing ships (they regularly dump or lose fishing nets which end up forming a decent fraction of all ocean pollution) or in poorer riverine countries with low standards of trash collection such as China, India, Indonesia, and Vietnam. Rich countries like the UK or US have rubbish collection rates approaching 100%.
Recycling is only sometimes better for the environment or cheaper than landfill. Depends on the item ... By the time someone has picked up that plastic container of peanut butter, driven it to a recycling facility, separated it into its plastic type, taken off the lid, fully washed it out in hot water, and melted it down in a specialized facility, we might have used less energy and produced less pollution just to make a new one from scratch.
Because of these realities ... — lids on containers, food still inside them, or paper not being dry— lots of materials that are collected for recycling are nevertheless never actually recycled and have to be sent to landfill. Lots of materials that are collected for recycling are never actually recycled and have to be sent to landfill. This is increasingly the case as developing countries start refusing to use their low cost of labour to do the dirty work of figuring out what to do with our recycling.
We aren’t anywhere near running out of space for landfill. The Earth is huge and we are good at digging deep holes ...