IE has only so many Euros and man-hours to spend on capital works. It can spend them on improving the lines where they can compete or the ones where they can't. Even with the current improvements Nenagh Branch needs way more to be competitive against buses in the M7 corridor - even against buses which replace train service during possessions! It is quite simply throwing good money after bad.
Getting back to the thread at hand, if IE redeployed the spend on the Branch to the Limerick-Athenry route there might be scope to deal with some of the speed restrictions necessitated by incidents at sight-restricted crossings such as
that recently reported on by RAIU.