Why would investment banks not care about their risky exposure to subprime mortgages? At the end of The Big Short, Steve Carell's character asserts that the banks weren't acting stupid, and that they knew they were getting a bailout so they just didn't care. Why wouldn't they care? From what I understand the bailout was just a bunch of big loans. Why would you not care about losing a bunch of money and having to take out huge loans?
The movie over-simplifies the large banks' attitudes somewhat. In reality, they differed:

some banks limited their exposure to junk debt (I will use this term because there was junk other than subprime mortgages involved). They'd buy up a little junk, repackage it into new instruments, and re-sell their instruments to clients. So their own exposure to the junk was limited, which is commendable. Their losses came a little later, when the clients who bought the repackaged junk sued them for billions of dollars and eventually won.

some banks were buying up more junk than they could use right away for repackaging - holding an inventory, intending to re-sell it eventually, and hoping to earn more money by holding the high-yielding junk meanwhile. This bet did not go well. (And they got sued too.)

a couple of banks thought they did not have junk exposure, but they were mistaken. One very prominent bank CEO went on TV to tell the public that his bank had no junk exposure. He might have believed it, but a few days later it turned out that all the repackaged junk that his bank sold to clients had a &quot;par put&quot; clause, meaning that the client could require (&quot;put&quot;) the bank to buy back the repackaged junk at face value (&quot;par&quot;). When the repackaged junk was trading at about 20 cents on a dollar, the clients massively exercised the option, causing the bank to lose tens of billions of dollars. (And they got sued too.)