Why do you never see Maelstrom on Invoker?

Generally when I play QW Invoker I build phase boots, drums, eul's, ag's (and force staff if I need to), but after that I'm a bit lost on what to spend money on.

I had the idea to pick up a Maelstrom, tried it out, and the burst it adds (especially with alacrity) is absolutely crazy.

Why do you never see Invoker players pick it up?

Invoker needs mobility, utility and the ability to use his spells as best as possible. Maelstrom doesn't help with that.

Do most players go Heart/Sheep simply because they feel like they have enough and want to up their survivability or mana regen?

Yeah, and Scythe of Vyse for extra disable.

alright, thanks

Inwakre best Hero! :D

If you like to try strange things,go for 3xQ,max,W,E and go for Alacrity and Coldsnap Invoker with a Midas 1st,Shadowblade and the a Desolator!
If you make it work, you will have a fun Time blasting your enemies in like 3-4 Hits :D!

Otherwise, i'd suggest you to go for :

Powertreads,Blink Dagger into Aghanims or Euls, then you go for Euls/Agha (depends on what you decided to go 1st after Blink).
Then there is a whole lot you can try!
Sheep or Orchid for some extra disable and mana reg.
Refresher, if you are really confident, for another fun round of Meteor/Sonic Blast/Emp etc.
You can choose and go for a more hitting Invoker, like you said, Mjolnir, then Assault Cuirass and a Desolator or Monkey King Bar.

That Hero is so versitile once you have his 2/3 core Items, so decide situationwise what you want to go for!

HF