To be fair, Hearthstone has less room for text, and has less need to be wordy because the computer will enforce correct interpretation of the rules. There's been plenty of cases where the Magic variant of a Hearthstone card would be clearer that the Hearthstone card actually is. For example, Yogg-Saron, Hope's End stops casting random spells as soon as he kills himself with one of his random spells. This isn't mentioned anywhere on the card, and it goes against the natural assumption of most players.
Hearthstone's wording is also inconsistent at times, like how Desert Camel says "Battlecry: Put a 1-Cost minion from each deck into the battlefield.", and Dirty Rat says "Battlecry: Your opponent summons a random minion from their hand.", or how Embrace the Shadow says "This turn, your healing effects deal damage instead.", whereas Auchenai Soulpriest reads "Your cards and powers that restore Health now deal damage instead."
In the end though, I think it mostly comes down to Hearthstone having less complex cards on average. For one it's a strictly sorcery speed game, which already eliminates a lot of complexity. It also has only one zone you can freely interact with, the battlefield, lacking direct guided interaction with other zones like the graveyard. Sure, there's cards like Resurrect, but the targets are random. A fairly simple card like
Reassembling Skeleton doesn't work in Hearthstone, because you can't actively look at the graveyard and activate abilities from cards there. I feel it leans a bit heavier on keywords than Magic to create unique cards as well (Houndmaster Shaw would never be a mythic in Magic). Hearthstone does make deft use of the fact that it's digital only to craft cards that wouldn't be possible in a paper tcg, like with Toki, Time-Tinker. Her ability is short to write out, even in Magic ("Add a random legendary minion that isn't from a Standard-legal set to your hand"), but the effect is completely impracticable in the paper world. Magic, on the other hand, uses its room for text to the full extent. Complex cards like planeswalkers, that offer multiple effects simultaneously, are neigh impossible to make in Hearthstone.
And I could go on and on. In the end, Hearthstone restricts itself heavily in multiple aspects of the game when compared to Magic to keep its card text short and sweet. Magic, through its lengthier, meticulous wording, offers the ability for far more complexity, offering a deeper gameplay then Hearthstone at the cost of accessibility.
PS. "Ragnaros, the Firelord can't attack.
At the beginning of your end step, Ragnaros deals 8 damage to a random opponent or creature or planeswalker an opponent controls."
PPS. "Whenever a spell or ability you control lets you choose one, choose all instead." (Entwine is a thing. I don't see why this couldn't be worded this way.)
