nikdfish, has the right idea, the Bowden tubes, PTFE liners, and Nozzles are consumables and you should plan to replace them periodically.
So far my Mk3 like to get a hot end rebuild about every 1000h or so, although if I wasn't swapping materials as much I would expect it to be reasonably higher.
To add to the higher temp thing, frequent swaps between high and low temp materials will also toast nozzles.
You end up with either burnt low temp material coating the inside of the nozzle. Or high temp material coating the inside of the nozzle that didn't fully purge when your attempting to print low temp materials. Either way the coating will keep the material from transferring heat properly and lead to the hot end backing up.
Also be careful of fiber infused, or glow in the dark filaments. If it contains a material harder than brass, it will rapidly wear your nozzle. In those situations you really do want a harden or equivalent nozzle.