If your PIN is something like a birthday, that is a random number to everyone except people who know you.
You only get three guesses before the card will be blocked. So even if I’ve maybe gone through someone’s bin to find out all their details, I’ve only got three goes to get it right. What might they have picked? Their birth year? Their day and month? But in what order? Month first? What if their birthday is in the first 9 days of the first 9 months? Have they just put zeroes in front? Maybe I’ve found loads of gaming stuff in the rubbish so their PIN could be 1337? Maybe it’s just the last four digits of their card? You’d have to be pretty sure before you make those three attempts.
To everyone apart from people you know, your PIN is a random number. Fraudsters often get your PIN by watching you enter it, either with a person watching or a camera above a compromised ATM/terminal with a card skimmer attached too. Then in this case it’s irrelevant if your PIN is your dog’s birthday or a number a computer threw at you.
How much bank fraud is through the use of PINs compared to the likes of just doing an online transaction that doesn’t require a PIN or old fashioned signature transactions? And of the fraud that has used a PIN, how much of that came from the card being skimmed and a camera watching the person type the PIN and a new card made? In which case your PIN being random or not is irrelevant.