Community

if  I'm spending 4 mana to cast a tutor, my deck probably could be built better

Sometimes there are abilities with plusses and minuses. Sometimes it's obvious that they even out ( Dream Fracture = Cancel ). But when it's not obvious, it's rarely costed as a drawback, because people who don't want to build around it can stick to the usual card ( Goblin Roughrider ), and people who do want to build around it are obviously willing to accept the drawback without getting a mana discount ( Hellraiser Goblin ).

It's clear that this card's ability of putting itself back in needs to be costed like it's a benefit. Ignoring the randomness of deck shuffling is very powerful.
In a combo deck, if they only need one more piece, they don't care that they put this back into their deck because they're going to win once they draw the combo piece anyway. While if they need two more pieces, they can use this card to find both of them even if it will take three turns.
Alternatively, this card can be used as a combo piece itself. Eg, with Time Stretch .
In a control deck, they can turn the card disadvantage into card advantage by putting Tidings on top every turn. Or they can use it to find their finisher, and if it gets killed, find a new finisher. They would only be using this kind of card at the point in the game where they have a ton of mana and have the game under control anyway so they drawbacks are irrelevant.

most combos don't equal instant win