Sunlight, humidity, acid rain, chemicals/mechanical-means (such as: abrasive fluids' impingement; car washing/drying)...
surely influences the degradation/longevity of LSP's...including Sealants.
But it is in my humble opinion that the biggest culprits (co-workers/co-conspirators, so to say) are: 1.)Biological-'materials'.
These include insect bodies, tree gums, and bird-droppings.
2.)The effects that base-coat-pigmentations have on the "performance level" of clear-coats.