There are limited resources, but there are enough resources to improve the architecture over more than a decade. And if they decided to avoid architecture changes, there would be nothing in the way of throwing lots of siloed software engineers at bugs to get more of them fixed. They're not lacking for money with so many customers. It's possible for them to set a much more inclusive cutoff.

They could have fewer bugs per feature than almost any other product after being stable and popular for so long. But they choose not to make that a goal.