Sure, they prevent you losing those things if the company loses more money than it has and the creditors want to come after you personally.
They don't prevent you losing those things if you invested your life savings in the company, and you mortgaged your home to invest more. Which are both things that people trying to get companies off the ground do, especially if they don't otherwise have the means to do so.
If you're considering the primary purpose of a UBI as being encouraging entrepreneurship, then sure, they're not that efficient. I do not consider that to be its primary purpose, nor have I yet spoken to anyone who does. It is one of many, many benefits to a UBI that should be considered.
They don't prevent you losing those things if you invested your life savings in the company, and you mortgaged your home to invest more. Which are both things that people trying to get companies off the ground do, especially if they don't otherwise have the means to do so.
If you're considering the primary purpose of a UBI as being encouraging entrepreneurship, then sure, they're not that efficient. I do not consider that to be its primary purpose, nor have I yet spoken to anyone who does. It is one of many, many benefits to a UBI that should be considered.