It might do the opposite. Imagine if the company was held responsible for the quality of the software regardless of how it was made. I suspect it would be much easier to meet any quality standards if software was written in-house.

It would get outsourced to the first provider who can indemnify the company against any failures in the software. Whether or not any provider would dare to provide such a service however...

However it happens, it still attaches a legal & financial cost to lazy security practices. And makes it actually in companies' best interest to do security auditing. I think that would be a net win for computer security - and consumers everywhere.