Have you ever come across unimportant but nicely done part of an application? I have observed this quirk myself few times.
For example in an e-shop, user preference settings can be oddly polished - feature that is mostly unused by me and I am willing to suffer through it once in a while workout impact on overall experience. However from development standpoint, updating user preferences can be tricky - there are many validations and you might need to integrate several external services to promote profile changes. The screen needs a lot of debugging and is heavily used by the developer to update settings for testing. Naturally the preferences screen gets nicely polished via multiple iterations and sheer need to work efficiently (eat your own dogfood principle).
On the other hand putting item to basket can be seen as straightforward task - update the cart, store it in the session and you are done. Do one test transaction to make sure everything is fine and you are ready to move on to the next feature. Of course nothing is as simple as it seems and lot of issues can go overlooked - What if I add items from multiple open tabs? What if I am already in the checkout? Unfortunately you will not notice as there are other features needing attention.
I see this example as an edge case bias in building UIs. The complex parts get lot of attention while the seemingly simple ones are typically handled in once and done manner.
Of course it is obvious which functionality brings more value to the customer and developers typically understand this, but being engrossed in the problem causes all types of myopic behavior. As a result, friendly nudging is sometimes useful.
For me this serves as a reminder to regularly take the step back when I am deeply involved in some problem to not miss the forest for the trees.
Also, keep in mind to always spend extra love on the main user flow.