No reason, really, other than just force something new, even if it's a '20 (I had an '18).
Part of me wanted to sell the truck when it still had some good value left and well before a new chassis update came live. I don't think the Gen2's will hold their value nearly as well as the Gen1 did and that always made me a little nervous. I paid over sticker for my truck when new which never sat well with me, and wanted to recoup as much of that as possible.
I might just go buy a Tacoma interim; yeah, it won't be the Ford, but they're simple, reliable, hold their value regardless of updates, and I personally think they look great. A Prospector might be fun, etc. etc.
I'm also negotiating on a new '20 right now. So far I've negotiated $2500 under MSRP, but looking for some more. If I can swing a new one at a low enough cost, I'll likely go that route as this has, hands down, been my favorite car.
Always happy to hear your opinion.
@Kyle Nezat, those are Method 17" 105 beadlocks wrapped in BFG 37" KR2's. Great tires, but highly not recommended if you do much driving on the pavement; the noise level is pretty abhorrent.