I get what you mean, but that's kind of what I was trying to get at! To get those headline low fares, you're flying basic on Ryanair (and I love them for it)
I do think though that a lack of seat selection on their site is a bit of an own goal though, something that's easily chargeable for. Would definitely be easy to charge for a table of 4, and I would imagine many families would be happy to do that. Could also do a system like Ryanair do where if you pre-pay for allocated seating, you can pick where you are, but if you want to save money, you only receive the allocation nearer the time and might be separated if travelling together. The only issue there would be making sure that families with young kids aren't separated apart.