Signal is a secure comunication app not a messaging app. All they do is optimized towards providing security, confidentiality, and/or privacy with a decent UX, but they make it very clear that the UX is on a lower level of priority. So since message transfers are a confidentiality risk they do not provide it.
Signal is an analogue of the tor browser, most people get diminishing returns after an adblocker/incognito mode.
