I think only one reason, they are very expensive to operate.
Indeed. Plus: vessels reportedly worn out from their hard work. Furthermore: bad maintenance, and inconvenient layout. Those things could be taken for granted in a good market, but alas, the market for used ferries is still really bad. The beach at Alang is currently full of "young" ferries which probably would have seen further employment in a different market: besides CARIBO and SMALLWOOD, there are currently: PRIDE OF TELEMARK (1983), EASTERN LIGHT (ex-SEAFRANCE RENOIR, 1981) and WESTERN LIGHT (ex-SEAFRANCE CEZANNE, 1980, completely rebuilt 1990).