Why doesn't android switch networks?

Question

Android

I have an android 4.0.3 phone with 2 sim cards (Ukraine): beeline-kyivstar and kyivstar (not voice, 3g).
3g is only in places in the city, in the subway only 2g. Constantly have to switch manually, the setting does not work.

Utel 3g, KYIVSTAR 2g - 3g kyivstar and kyivstar beeline respectively.
To switch - you need to open the search for networks (2 minutes of searching) and select the one you need.

Already tired of doing it.
1) Why might the auto switch setting not work?
2) Are there programs for independent fast switching?
3) Is it possible to write it yourself if item 2 is false?