Just to expand a bit on the other answers, being the sole developer (as opposed to the jack of all trades of IT, which will ruin your focus) can be an interesting experience for learning, as opposed to simply a stagnation sentence.
Take into account some established teams don't necessarily follow worthwhile practices, so you get to avoid that possibility entirely if you're fresh in the business where you can't go cherry picking those.
Being the sole developer among people who just want things done lets you implement stuff however you want, and with the right mindset this can either benefit or doom you.
This is by all means a double edged sword because:
- You have freedom to try out new things under your own clearance
- Consequentially, you also have freedom to do an awful job.
You need to plan to move on eventually:
- You will reach the stagnation phase at some point. You don't want that.
- The idea is that the sole developer actually has a team: themselves and "the next guy". Keep your work sensible, not just for you but others.
- A sole developer that never moved on is simply someone who has blown up a hole on the ship, shaped like themselves. Now they're the cork; and a pricy one.
Another thing worth mentioning is that, as contradictory as it may sound, being in solitude and having to think for yourself for a while may give you desirable traits as a leader and overall problem solver, as portrayed in this speech by William Deresiewicz at the WP Military Academy; here's an excerpt:
[...] Institutions are being guided by people who are good at keeping the routine going, but bad at thinking; specifically, bad at thinking for themselves. The solution, then, seems to be to teach people this trait. However, “thinking” isn’t something that can be taught, it must be done alone.
Ideally, a great sole developer will make themselves replaceable and eventually move on to become a very valuable asset within a team with their experience in decision making.