JetBlue does not have any domestic interline partners, so it is correct that they cannot put you on another airline.

Weather can cause problems down the line. It could be that the plane arriving at LGB was delayed due to weather. The other thing is, "weather" can also include high winds, windshear, etc that you won't see on a weather map.

The best they can do is either refund or rebook. Larger carriers may have more options with connecting flights to your destination, but if it all else fails, carriers like United would also tell you the same thing, either cancel for a refund, or rebook.