I've written about the upsides of working on multiple products, so today I'll cover some of the downsides.
The importance of focus has been preached to founders forever, and the lack of focus is clearly the biggest issue with working on multiple products.
When your full effort is behind making one product work, your mind will constantly be soaking up relevant information and thinking of ways to make it happen.
Less likely to quit
A friend runs an agency that builds bespoke products for startups. I once asked how often the startups they work with go on to be successful and they said something along the lines of "the ones that became successful ate shit for two years before getting traction."
That seems to be super common. It frequently takes a year or two of focussed effort and learning to make a startup work. When working on multiple products, it's easy to switch focus at every hurdle. If you're only putting a few weeks of effort in at a time, those two years could become more like five.
You story becomes more complicated
When all your energy is behind one product, you become clearly associated with it. Your friends and family have at least some idea of what you're working on and they can find ways to help you succeed. When they come across someone who might find your solution helpful, they can recommend it.
With multiple products, that's more complicated. It's harder for friends to send potential customers your way when they're not sure what your focus is. You don't know which product to mention when asked to introduce yourself to a community. It's a more complicated story to tell.
I'm sure there are more downsides I'm not thinking of, but I still think working on multiple products isn't a bad idea in some cases, especially when you're in a phase of exploration.