Because the fields are there for humans, in the packet itself it’s a 32bit integer, and you can’t just arbitrarily make the src/dest fields in the packet bigger— it stops being IPv4 then.
I'm pretty sure the person you're replying to is saying that IPv6, should be IPv4 but longer, which is not at all an uncommon opinion, even if it's a breaking change to the IP protocol. And I'd argue there would've been incredibly strong benefits and much wider adoption if they did this. Sure, you'd still need new networking gear and software support to handle it, but the change is relatively simple (and potentially more easily backwards compatible), especially compared to all of the baggage that came with IPv6.
It's a fact of life that working with networking that we'll have to work with IP addresses at some level. It's easy to tell someone, "hey try typing in 'ping 8.8.8.8' and tell me what you get".
The readability of IPv6 is, in my opinion, worse with repeated symbols and more characters to remember. The symbols that were chosen were also poorly thought out. Colons are used in networking a lot of times when you want to connect to a service on a particular port, so if you want to visit 2001:4860:4860::8888 in your browser, you have to enclose the address in square brackets.
