These companies aren't missing the opportunity out of choice.
It's all down to licensing agreements with the studios, Eureka even mentions this in their booklets. In their case, Eureka simply distribute titles from other studios, so for example Repo Man and Silent Running are owned by Universal. Universal demand region locking from Eureka in the hopes that overseas customers will buy their own release. Whether that works or not I don't know. It probably does to the average consumer.
With someone like Warner, they distribute their titles worldwide in the main (Watchmen was Paramount in the UK), so don't bother with region locking. You can buy a Warner title from anywhere in the world and it will be region free (I believe). It's the same even from the aforementioned Universal. For the titles they hold worldwide distribution for, say, American Pie, Fast and Furious or Jurassic Park then they're region free.