It is a card that can 'do' so much, so it fits in several decks across multiple formats. It's ability to act at instant speed is the key to its utility
Its a creature
Its an artifact
It can be a creature death trigger, creature gy trigger, artifact destruction trigger whenever you need it
It can ping creatures without tapping
It has the ability to hit planeswalkers without tapping
It can hit players directly without tapping
It can be played early or late to maximize value depending on mana available
Its a mana sink, adding +1/+1 counters when you have nothing better to do
It's a combat trick if you pump it, or if you ping during blockers phase
Target for scarab god
I suppose it's also a trigger for the new 'historic' mechanic
There are more, I'm sure. It's a great card that has demand from other formats than standard. It has been near this price before and as low as $10. Great pile to sell or sit on. I'd consider selling some now that is back up in price before the upcoming rotation in the fall hurts its demand. Sit on some as it has value in other formats.
I'm not sure what caused the recent 50% price increases. It's in conjunction with the Challenger deck
release which should have had a downward effect on price as more became available.
EDIT: UPDATE - I understand UW
flash historic is a standard deck with internet hype that is enabled by new dominaria cards; it runs a playset of these. That's the cause of the current spike. Price started going up around dominaria
release. Challenger deck reprints had zero effect on value. Last little spike was during ixilan to pick off low toughness pirates/merfolk/vampires and
enrage dinos.