There is no contract between you (the licensee) and the licensor of the software. The creator of the open source software just says "here's the software, you may use it if you like, as long as you fulfil some conditions. ". No contract, no liability.
I think the developer would only be liable if they intentionally created software that causes damage. (Which has happened, some open source browser plugins have recently been modified to run bitcoin mining software, or worse. I suppose the miscreants could follow all the GPL rules or whatever license is used).
