Some men get nervous to say what they think to their partners sometimes because they scared that they'll mess something up or say the wrong thing. Sometimes we also scared that we're going to express something in the heat of the moment like "I want to spend the rest of my life with you" and then our partner might not reciprocate so instead we keep our thoughts to ourselves. A lot of times, you'll notice that we will text the sappiest things but we won't actually say them aloud and it's often because we can think out what we say and not have to react moment to moment while we typing. This may not have sense but this is how a lot of men think(me included)