Why shouldn't you be able to keep using it on Wi-Fi only?

So Apple should try to support a phone with 256MB RAM and a 400Mhz processor in 2007 that doesn’t even work on any cellular network?

What do you expect to do with it? The 2010 first generation iPad that came out 4 years later could barely handle modern web pages by 2011.

You can if your router supports it

Yes, but if you can't get security updates for it, then you can't do so safely.

2G is still alive in Germany.