Because the exact information isn't actually necessary for the vast majority of people; that's why our site is set up with tiers and the like. Since it's usually just the general range that matters, not the specific values.
sort of, although this does completely fall apart with big tiers like high 6-A, and even more so with supermassive tiers like 4-A
but hell, even street level alone has multiple one-shot gaps within it, and wall level has a shit ton
Cluttering the page with information that most people don't need, and which often looks ugly with the completely unnecessary 12 decimal places a lot of users maintain, isn't great.
I haven't actually seen any cases where people include 12 decimal places
here are some more examples of this formatting being put into practice
Naruto
just looking at this otherwise large profile for under 10 seconds, I was able to easily find the tier and calculation value of his base, sage, and rasenshuriken. Extraordinarily easy.
Jumbo Josh 
as you can see, this is a good example of the formatting having absolutely nothing to do with clutter, as even with simple and short justifications, the calc value doesn't even take up 8% of the space used in the Attack Potency section
Mash
once again, in an otherwise very large AP section, it literally took me
less than 3 seconds to find his base form's initial value.
so, when put into practice, I absolutely do not see any reason to deliberately go with the option that takes longer, just for the sake of saving 2 words worth of "clutter" space.
Specific values only really matter when we get down to making matches, and even then, most characters within the same tier can match with each other just fine.
The bolded section is still irrelevant, since knowing who even has a 2x AP advantage is typically a big deal in versus threads. There is rarely a situation in which you shouldn't be seeking the exact AP values of characters when making a vs thread.
With my personal preference out the way, I've responded in this way for the purpose of being as objective as possible, since reiterating my opinion on what looks cool won't be of much help of course.