My last phone I kept for about 5 years. I had two issues:
software support had ended
the battery was severely degraded
fortunately there was a local shop who'd replace the battery (it wasn't a fairphone so I couldn't do it myself). If it wasn't for the software support I'd have gone that route and would be still using it now. It worked perfectly well for my use case. Unfortunately, I ended up retiring the phone and getting a new one.
The whole philosophy of Fairphone is keeping it as long as possible through long term maintenance and access to spare part for self repairs. Fairphones are "outdated" almost at launch in terms of hardware in comparison to most phones on the market because this is not what we (fairphone customers) are looking for.
Exactly! I don't care that I don't have the most modern gadgets on my phone, I didn't have them before so I will not miss them. To me being unable to replace my battery or having to get rid of my phone because the OS is outdated is unacceptable and stupid and I will gladly sacrifice having a 1gigapixel camera or being able to take my phone in the shower.
I think for the target market, it actually makes a lot of sense. Hardware from 2016 is still perfectly useable for most purposes, except that in the android world you might have a hard time with compatibility because the software is very old at this point, and the battery would be pretty shot. This phone has solutions to both of those problems.