Apps to SD functionality was discontinued by Google on all Android versions from 4.2 Jellybean, I think it was. I think that their thinking was probably that, as phones internal storage had tended to increase by that time (what with flash memory becoming cheaper), abolishing the function would abolish the crashes that it sometimes used to cause.
It used to be allowed on things like Android 2.3 Gingerbread because even good phones like the SE Xperia Arc S only had about 386Mb of internal memory, so apps-to-sd was quite an essential feature, but I do remember my apps sometimes suddenly cease to function for no apparent reason.
4.2 Jellybean probably requires a minimum of about 4Gb internal memory to run and Google probably feels that this is enough internal memory not to require keeping apps-to-sd functionality going and the inherent problems it can sometimes cause.
There's also the fact that Google has been trying to advertise and advocate the use of Cloud Storage lately, particularly Google Drive, Google Music and Picasa, so they'll have figured that if you use lots of your available internal storage for apps, some of which are around 1Gb now, then you'll be more likely to use cloud services for your multimedia files and so they'll can get a more accurate statistical handle on what music, pictures and video content the public likes to collect, for their advertising and the kind of statistical analysis uses that Google deal in.
As another aside, it's ommission will probably help drive the upgrading of smartphones by people to ones with higher internal memory and specs, so in turn that'll be good for both Google and their manufacturing partners in a kind of capitalistic, profit making and business sense type way.
Anyway, those are my theories as to why they discontinued apps-to-sd functionality but I can say for definite that on the Android versions like 4.2 and 4.4 that the Xperia Z1 runs, apps-to-sd functionality has been disabled and discontinued by Google and is now a thing of the past and that won't be getting superceded by any software updates by Sony at any time, I don't think.
