So, most banks have had this fight with their customers. In the 80's and 90's as debit cards became the norm and check writing started to become less of the norm most banks processed transaction in the way you wish they would i.e. smallest to largest. Once it was clear that the overwhelming majority of people would be performing the majority of their debit transactions with these cards most banks switched to the current system of largest to smallest due in large part to public outcry for this change. The bottom line being that they ain't changing back at this point.

Also, there is no fraking way for a bank to process transactions "in the order you spend the money." Even in today's digital age it still takes your bank about a week to process a debit card purchase from start to finish. This is why you have pending transactions on your account. Because the bank can track in real time that you swiped your card at a given merchant, and thus temporarily set that money aside. But then the merchant's card processor has to actually ask for the money, which is then transferred to the processor, then to merchant's acoount. And there are multiple stop gaps in place just in case you or the merchant need to make amendments to the final transaction (adding gratuity, same-day returns, etc.). This is also why when you do a return at a store it can take 8 to 10 days for you to see the money in your account. Because that's how long it can take for all the different background processes to take place in either direction.

Source: former bank employee (and trainer for all this and much more).