Geez, I need to re-sign in every time my mobile data switches IP?? IPs are NOT static. Mobile networks change IPs CONSTANTLY. What if I use a VPN (I do) and my IP changes constantly? What if an IOT device on your network is serving as a public residential proxy that anyone can use (more common than you may think), or hell, you have CGNAT and your neighbor does? What if an entire country only goes through one IP[1]? Have you done this in practice?
[1] https://en.wikipedia.org/wiki/User:82.148.97.69