I think it's because he was very young when his father died and mother was bedridden. The sudden responsibility of becoming
the man of the house was on his young shoulders. He had to become stronger and mature before age. Yes Masi Sa was there but he grew up quickly to share the responsibility of their family together. He couldn't afford to feel sad and heartbroken otherwise his family would worry about him amongst other problems. So he stopped trying to feel that way and with time, forgot how to express himself other than in simple and few words. (Like he does with Kanak, whenever he talks about his feelings or their marriage, he's very quite and straightforward, unable to use his emotions effectively, that's why people are scared of him, that's why his silence bothers Kanak).
That's my take on this topic :p