(BREAKING BAD) Why didn't walter white put his money earned in a bank account?

The same reason real-world criminals don't just do this: banks are required by law to report suspicious transactions, including cash deposits above a certain amount, large amounts of money with no obvious source, and other things. This is also checked against taxation and employment records, and these days with everything digital it's very easy for the authorities to do that.

Remember, Walt was supposed to be a high school teacher, with an official income of only about $40 000 a year. If he went and tried to deposit 80 million in cash into the bank, it would not be long before the authorities started asking questions about where he was getting it from, which would almost certainly result in police attention. There's also the possibility that the IRS could "audit" Walt and look into his affairs. If he seemed to have more money that he was officially declaring as income they might have investigated him as well. You can't just write "drug money" on your tax form and get away with it.

That is why Walt set up the car wash- this was an example of "money laundering". What he was doing there was running a legitimate business (the car wash), then when he deposited the profits, he would also add in some of his drug money as well, so he could say it was all carwash profit (e.g. if the car wash was really making $1000 a day, for instance, he might write down it actually made $1500 and add in $500 of his drug money). Then he could indeed put it in the bank and use it legally- and that is what he was doing. The problem he had was that he was making far too much money to launder all of it (no carwash that size would make 80 million a year, so he couldn't get through it all).

Real criminals have the same problem and use the same tricks to get around it: if they just deposit stacks of cash into the bank without a good explanation as to where it's from, the authorities are very good at detecting that and criminals who do that will almost certainly get caught. So instead, they often open up legitimate businesses that make some profit, and they disguise their illegal money as profits from their legitimate business.

Of course, the police do know about money laundering and they often try to investigate it as well. For instance, if Walt's car wash seemed to be making more money than it should have been able to, that could have resulted in attention from the cops. Also if the cops think someone is dodgy, they might look into their activities to see if anything else is suspicious.

Logic doesn't apply to Hollywood.