Let's give you a very simple example. Adrenaline. The whole mechanism, interactions of adrenaline with various thing such as steam machine, poison, or antimatter, take a whole 2 pages to explain correctly. (believe me, as wiki editor, i've seen it countless times.
First, there's NO way you're gonna make those two pages fit on the card.
Second, discovering the mechanism of that card is part of the fun of using it. It's not laziness part of the develloper to make a card complicated with very little text, it's laziness of the user (and community, if they all had that opinion) not to test.
Other examples : mutation, fate egg, lobo (Oo it doesn't remove passives?), flying weapon (what are the stats of teh weapon?), Bone wall (oh, so it replaces?), iridium warden, Dissipation shield (not field), Chaos Seed, Pandemonium, Discord, Catapult, Sanctuary, Nymph's Tear (interaction with QT?).