You've been downvoted, but I think that's a fair take. There will always be tension between security and usability; it's difficult (impossible?) to do the absolute best in both metrics.
Signal's development team can decide that they prioritize security over usability to whatever degree they like, and that's their prerogative. That may result in fewer users, and a less than stellar reputation in the usability space, but that's up to them. And if we (the unpaying user base) don't like it, we are free to use something else that better meets our needs.
Maybe an answer is to have a control for each message that you can set to plain text or encrypted based on a cloud backed up key of encrypted based on a key only on this device. The you could message "hi mum, running late" without complications while being able to hard encrypt when you want?
Signal is already complication free (at least until your phone falls in a lake) making the control useless.
(And you probably don't need to worry about losing the 'running late' message in the lake... The need for good encryption and reliable backup on any given message is likely somewhat correlated.)
Signal's development team can decide that they prioritize security over usability to whatever degree they like, and that's their prerogative. That may result in fewer users, and a less than stellar reputation in the usability space, but that's up to them. And if we (the unpaying user base) don't like it, we are free to use something else that better meets our needs.