The S10s are not eligible because they came out alot earlier in the year than the S10lite and are in the category of not eligible because of this. It has nothing to do with specs as the S10s would be more than capable to upgrade
I also still have my S10 and can agree that they are a good capable phone but I am pretty sure lack of updating is all about Sales and making money and nothing about the phones not being able to function with the new UI updates
Absolutely the S10 series can support One UI V5.0 > V6.0 and more.
It's purely a business decision, SELL SELL SELL!
I get that Samsung is a Business, but the LEAST they could do, would be to Unlock the Bootloaders on devices they will no longer update.
Majority of people won't likely bother anyway, but at least people could then easily Flash Custom Roms & get all the Tweaks & Security benefits.