Those same networks are still functioning with much less proportionate overhead.
They're also much more technically competent. Look at how the different networks handled the cross-protocol exploit a few years back where a well crafted link could cause the browser to connect to irc and spam. Most other networks required a PING/PONG on connect so they weren't vulnerable. Of the networks that didn't, they were able to mitigate that within minutes to hours by either a simple configuration change or a firewall rule. Freenode was unable to do anything for months. Their solution was to rewrite their entire ircd and tell people not to complain about the spam.
https://netsplit.de/networks/top10.php