The 5 also has 2GB more RAM, 200mAh more battery life, a 90hz screen with more contrast (1M:1 vs 100K:1 ratio), aluminum vs. plastic body, and Gorilla Glass 6 vs. 3.
It also looks like the 4a 5G has two sub-models for different networks, whereas the 5 has them all in one model. So if you desire more portability between 5G networks, the 5 is a better option there.
That's pretty much all I could see as notable differences. Not saying any of that is worth the price difference, but perhaps it explains it a bit. I am definitely going to wait for the inevitable Black Friday deals they do shortly after release. They discounted $200 in past years, which makes the 5 much more palatable to me.