samefag here, now that I've thought about it, I am pretty certain these ip range bans really are intended to get more users to buy 4chan passes.
That would also explain why they've made the captchas increasingly tedious. Stopping spam is just a false pretense.
If this was 2007, or even 2011, I probably would have considered paying for an account, but these days 4chan is hardly even worth spending more than a few minutes on, let alone paying to post on. On a semi-related note, anyone else remember when "4chan gold account" was just a meme?