Possibly because people have been screaming out for a decent alternative to PayPal that is backed by a big name.
Nochex is a good UK payment method but UK only.
Google Checkout is gaining in popularity and fingers crossed Amazon starts to beat on PayPals door.
Why do people want alternatives - you just have to look at the amount of people complaining about them and their somewhat bizarre claims process. 'Yes, you won the claim but sorry they don't have any cash in there so the case is closed, we did our bit - chin up and please continue getting butt mugged but this and our fees.'
I try to do Google Checkout as often as possible now.
There are plenty of other payment processors - Alertpay, eGold, YourPay, TrialPay and everything else but 90% of the alternatives are not backed by big names and will never touch PayPal unfortunately.
With Amazon and Google on the map, I hope they come stomping over the horizon and kick PayPal where it hurts - in the wallet.
The more well known online stores that use the likes of Google / Amazon (well, the smaller well known sites not something big that has their own merchant accounts etc) the more the dent will grow in PayPal and they may actually take a step back and think about their cruddy service.
Of course, just my opinion