Why does he love tickling me?

so my boyfriend is constantly tickling me! im extreme ticklish especially on my stomach. he is always findin a way to tickle me , like pinnin me down or tyin me to somthin stuff like tht. im okay with it i jus wanna know why he tickles me sooo much??? one time we were on the couch and he stradled me , used one hand to hold my wrists above my head and the other to tickle me lol