what you are expecting is idealism but it's all politics now, every party looking for their interest.
Congress knows they will lose even those 8 seats if there is re-election now so their best play would be to go with AAP. In case AAP does good then congress shares benefit if AAP doesnt do good work then congress will get regain some lost ground. In first case BJP will lose and in second AAP.
BJP knows they wont get support from other parties and can't break other parties as it will send wrong message in public. But they also know that 700 liters of free water to everyone and 50 % drop in electricity cost is very very difficult (esp in 3 months) so they will let AAP form government and come down heavily on them when they fail. BJP will come in majority if AAP fails.
Also AAP will be busy in delhi now so their affect in loksabha elections will be limited so AAP does good or bad BJP wins overall.
AAP is doing this sms natak so that they can tell people later that it was your wish to form government.
In my opinion AAP is in most difficult position, they would have benefited if their was presidents rule till may next year, they could have focused on loksabha elections in that case and also would have come in majority in delhi.
It's interesting game these parties are playing, lets see how it pans out.