The idea was that they were not meant to be a crutch you overrelied on when levelling through the game and just something you called on the short term when necessary (SE did want you to play with others as well).

Also you can easily extend their duration by simply feeding them another clump of gyshal greens while they're out/summoned (I think the time that it can be extended to is an hour). It's not that hard to buy a stack from the npc vendor in any city and then map it to your hotbar.