why not just ask them? i think it's completely reasonable to do so. you may say something like, "i'm really excited about working at your company. it sounds l

why not just ask them? i think it's completely reasonable to do so. you may say something like, "i'm really excited about working at your company. it sounds like a great opportunity and the interviews have been promising. i'm willing to wait until april for the right opportunity, but would you be willing to share the reason you wish to delay? this would help me since otherwise my imagination may run wild with explanations, and with any good long term relationship openness and communication are valued. thanks!" or whatever phrasing you like.