I can fully understand why big company does not want to tie itself to app engine or other Google services, especially if they are able to keep their own infrastructure. If they are European company, having customers data on app engine might not even be legal. Google was not able to guarantee that they will not move data over border and there was regulation about it. Not sure about current status.

Big company has to maintain many projects. Managing too many technologies and contracts with too many suppliers is huge hassle.

Outsourced maintenance was probably simply incapable, there is huge amount of parasitic service companies living off typical big companies decision making faults. It probably had nothing to do with technology. Long term before deployment is also probably product of big company processes, other projects competing for administrators time etc.

That being said Python + app engine + backbone is much easier technology to start with and learn then java spring mvc + sencha. When you do small project in isolation, then former seems like much better choice. Those big frameworks usually pay only if you do something big.