Why would they do that? (Not a rhetorical question, just curious). It would suffice to block UK IPs for compliance, if visitors use a VPN to circumvent that Imgur would get more traffic and more ad revenue. No reason to put extra work into blocking those users.
Gives them proof they did their best to "protect minors" even if they circumvented the GeoIP rule: someone trying and realising it still does not work might get X percentage to not bother further thinking there was something smarter at play and not just GeoIP (which there is).
Could be for performance? Basically cache the group lookup result into a signed cookie that can be checked at the edge rather than needing to do a geoip lookup for every request.
