Your kids inherit the stock at its current value and immediately sell $10M worth to pay off original loan

And the bank says "um, what about the rest?" In the 1970s and early 80s the inflation rate was, at times, above 10%, so your loan's interest rate would have been above that. But say on average the loan's interest rate was 5% per year over 30 years... the bank isn't going to be content for just the original $10M.