As in they log in one day and have 3mil.. or they have 3mil period? Still 3 mil isn't a ton. Incase you just missed it there was a 3x sp cap event going on recently. This let you earn 570k active Sp in one week, or around 855k with a booster going. With the standard passive SP for a week thats almost 1mil Sp in a week durring the event.
Another explination for your quick SP is that they haven't played in a while and their passive SP built up over the months. If you made a character at the start of the beta you can expect 4-5 mil sp from passive Sp alone by now.
Only other explination I have is they haven't played since uprising came out and their skill points have not been spent yet and they are just finally noticing it.
Other than those optiosn I've not heard of millions of free SP falling out of the sky.
"That is not just scraping the bottom of the barrel, that is lifting the barrel up and poking some of the slimy sludge growing underneath the barrel."