Latin Wikipedia and many other modern (Classical?) Latin texts use "u" for the vowel /u/ and "v" for the consonant /w/, but "i" for both the vowel /i/ and the consonant /j/. This practice is more common than having both an i/j and u/v distinction. In the Middle Ages, it seems that u and j were used as a variant form of v and i based on the position in a word, irrespective of whether it was used as a vowel or consonant, so it's not as though u/v is different from i/j in that regard. Descendant Romance languages like Spanish and French use j for consonants, and even Italian which doesn't use j uses it for Latin loanwords (using it to represent /j/). Why is it common in modern Latin texts to distinguish u/v but not i/j?
I think the answer is plain: While consonant i is always a semivowel, non-classical (e.g., ecclesiastical) Latin does not treat consonant u as a semivowel. (See also this discussion.) Consequently it is really annoying to read Latin in many pronunciations, including those in universal use (modern scholars aside) since late antiquity, if v is not distinguished from u. There is no similar difficulty with i.
To translate a bit, when these consonants are pronounced like the English y and w, they are basically just slightly modified (highly shortened) versions of the vowels, so you won't sound like a fool if you initially take them as vowels when reading. (Think of why French oui is spelled the way it is.) It's no more difficult to read semivowel i and u this way than it is to read diphthongs that don't have special symbols. On the other hand, the English v sound, which is what consonant u began sounding like at least 1500 years ago, is a fricative and doesn't sound remotely like a shortened u.
There are in fact many scholarly editions of Latin texts that do not use “j” and “v” at all, and there is certainly a logic to this. On the other hand, even experienced Latinists can be forgiven for being taken by surprise by spellings like iuuenis or iuui and preferring the unambiguous juvenis and juvi.