Guy I’ve been seeing has started to message at least once every day. Why?

Yes, stop asking him that question about some commitment.  Close, committed relationships happen over time not immediately.  I don't understand people who want an instant commitment. 

Maybe he just has more time on his hands these days. That a gentleman wants to spend time together, wants to spend more time phoning and chatting, doesn't necessarily translate to him also wanting to get more serious. Even if you two are seeing each other every day, it doesn't necessarily mean that he wants to be more serious. When I was dating Brian, for a while we were having supper together every day and sometimes breakfast together. But he was still the same "not marriage material" Brian he was when we only seeing each other a few times a month. 

It's not the quantity of time together than makes the situation between two people a relationship. It's possible and non unusual for two people to spend a lot of time together but not have much of a relationship. A serious or long lasting relationship is about trust and respect, about mutual support and understanding, about being able and willing to work out conflict constructively instead of fighting. People can spend a lot of together without there much trust, respect, mutual support, you know? That not a relationship -- it's just spending a lot of time together.

A serious or long lasting relationship is something that evolves over time, not a matter of "OK, we can be serious." 

In my case it was still a friendship, despite of talking for hours every day.

It's because I've stupid questions like Taht that ya is shutting