Why can't a person just play ukulele because it's enjoyable?
for most people progress on an instrument is part of the enjoyment to make progress of any sort, a little bit of effort and practice is needed[ this is what i interpret as taking seriously]. beyond that ..well there are degree of seriousness, i suppose, but how about just regular practice, checking tuning. I am not asking for virtuoso performance but just some respect for audiences
some may want to play for an hour a day some may want to play for ten minutes a day. even ten to 15 minutes a day will see improvement, in my experience as you improve it becomes more enjoyable
not taking it seriously means not bothering to practise and not bothering to pick it up and play it in private, not bothering to check your tuning etc.
well that is not enjoyable for listeners.
Personally. when i play i try to do my best i practise[ the amount can vary] and performances can vary [not just because of practice , but bio rhythms etc]
Finally, i would not find it enjoyable to be given any instrument and told to play it if i had never practised on it.