I was expecting follow on too...
I still didn't check his press conference so I can make only educated guess, He might be thinking of giving seamers little more rest because it's hot and India playing with 3 seamers. 2 of them looked slightly uncomfortable in the first inning despite their short spells( Ishant due to heat and bumrah due to cramps) and by doing so giving batsmen another chance to get their forms back, which failed but they added 160+ runs on scoreboard. It ensures that India can't lose the game from here. Tiny chances for windies win.
India coming to bat again also means windies had to field for extra 50+ overs in heat, which is not easy deal considering the fact that they didn't get to rest much in this test match yet. In 3 days gameplay they spent max 3 hours in the dressing room.
There was no rain factor in his mind. And there was enough time to windies batsmen to comeback. There is always tiny possibility that some windies batsmen could fight back in case of follow on. Result tired bowlers leaking runs.
We are still in 4th day and I am expecting windies to show some resistance because pitch is becoming easy to bat on with little support for bowlers but they have 2 full day to get them out plus Indian seamers are fresh and got extra breathing time-out.
PS : ignore the typos using phone