What could be the reason why a guy is not replying to texts?

You are probably the best placed to get a feel for how your conversation goes.
Also best to ask him.
It can be a number of reasons, not always negative.

Cuz he's replying to some other bitch. That's why.

There could be any number of reasons. How long has it been since he replied?

There are many reasons - good and bad. Only think about the good ones, though!

He doesn't want to...only reason I can think of...when a guy wants to answer he does.
I have had both type of responses...

He might be gaming you.

context! like how long since reply are you in same time zone what is sleep schedule is he working is his service interrupted i would not assume anything... if days go by then it really doesn't matter why they lost interest but if they come back with explanation i would believe them the first time but if they keep doing it with more and more improbable explanations, then let go for they are deceptive.

You aren't giving him enough time

He's busy maybe

He’s not into you

Maybe he died

Playing hard to get, can't be bothered with trying to care rn, otherwise preoccupied, not that into you.

He's either busy, or he's not that into you depends how he responded to your text before.

Busy, if it's night, sleeping, maybe he's at work..

He's sleeping. He's playing the field. He was arrested in a protest. 🤷

Maybe he's nervous?

I reply most of the time

He's asleep.

He is GAY

He's either interested in another girl, he's gay or he's shy and wants to but is communication skills suck.