@Richard470 There are HUGE penalties for hosts who cancel so the system is not one-sided. However, I completely understand when there are travel arrangements such as yours, it can be anxiety producing to see a cancellation review. I suggest you send a message to the host about your concerns and see what response you get.
Unlike a hotel, individual host circumstances can affect their availability. Sometimes there are health issues or home issues that require the host to cancel. If you need the guarantee of a hotel to feel less anxious, that might be a better way to go. However, please know that Air BNB will provide great support to you should there be a cancellation. Also, you might consider travel insurance as well.
San Diego is a wonderful place to visit and I hope your holiday is a wonderful one!