So many people treat texts like they're synchronous, though. Haven't you ever had people send you follow-up texts half an hour after the first one to "remind" you to reply? I've found this to be really common.
Politely remind them, when you do get around to following up, that unless it's critically urgent (in which case they should call) you will only respond when you can. Which is not always immediately since you have other obligations (work or family) or may be involved in a task where you can't (commuting, when we did that sort of thing).