Question about rimming?

i feel really strange putting this on here but i cant ask anyone else..but why does my bf like rimming?..i love him loads & feel completly comfortable wiv him. so i am ok with him doin it, bt im not very experienced and i cant see why he wud actually wana do it. he says he loves every single last bit of me an wants to kiss everywhere...he says he feels obsessed wiv my bum cuz he likes it soooo much! even so, i dont know if i will ever really understand why he wud wana put his tongue up there. i certainly wouldnt do that to him but it doesnt mean i dont love him as much. iv tried askin him but he laughs and doesnt really know why himself. he says even he thinks its weird!! can anyone help me? why do ppl like doin this?