The big reason is that you’re choosing to spend several hundred dollars to put your still perfectly performant phone in a land fill so you can have a percentage or two more performance.
Your dial up comparison is not really a fair comparison, either. The S9 is not dialup in comparison to Samsung’s new galaxy phones. You’d have to go down to like a BlackBerry or a Nokia flip phone to have that comparison make sense.
Let’s compare the S9 to the S23.
The S23 has Wi-Fi 6E support, Bluetooth 5.3 support, twice as much base storage and RAM, 5G support, an in display ultrasonic fingerprint sensor, 3 high resolution cameras, 120hz refresh rate, twice as fast internal storage, a 33% larger battery, a much newer version of Android and to top it off a processor that’s roughly 3X as powerful as the S9.
So to me it might not be fair to call the S9 dialup but I would say a comparison between broadband and fiber is pretty accurate. At the very least the other features are worth upgrading for if not the speed. Now I suppose the S9 is still a perfectly good phone to be used as just a phone but these things are really portable computers and the increase in processing power becomes tremendous in a short period of time.
Does your home router support WiFi 6e? your accessories BT 5.3? Your phone carrier stable 5g?
I can understand the battery and the screen improvement. But I also don’t think it’s as drastic as you claim.