Why do some people say "v" as "w"?
It's hypercorrection.
Germans can pronounce the English 'v' just fine, they happen to write it as 'w'.
So the freshman English learner from Germany will pronounce (using English orthography/pronunciation) 'water' as 'vawter'.
They'll then start to associate the 'v' sound with a mistake.
So the sophomore reasoning, which results in fixing some problems, for a German speaking English will be to change anything that sounds as 'v' to a 'w'.
Even though 'vector' is written with a 'v' (and pronounced that way in English, a German might over correct and 'fix' the 'v' and use the 'w' sound instead.
We have a tendency to think that speakers of languages that have a similar consonant phoneme must pronounce it in the same way, but this is not so. For example, both Czech /p/ and /English /p/ are unvoiced labial stops, but the prevocalic English /p/is aspirated, and the Czech is not. As a result, Czech speakers producing the word pan with an initial Czech /p/ may sound to an English listener as if they saying ban. Trained phoneticians producing narrow phonetic transcriptions of the words produced by Czech and English speakers would use superscript notations to show this, but they would use the same phonetic symbol, [p], in both versions for the one to which they added superscript.
It's a similar situation with the /v/ sound. Most speakers of English pronounce their version of this with a degree of friction as the air passes between the lower lip and the upper teeth; Most speakers of German pronounce their /v/ with much less friction. If they use the German sound in an English word, it can sound to an English listener like /w/.
English novels are filled with Britons who say v for w, and w for v. They are neither German nor Indian, but characters like Sam Weller and his father Tony, in "Pickwick Papers" constantly make statements such as "Vell, the gentleman must have wanished before my eyes. Wot do you think, Samivel?" (The last being Dad's pronuciation of Samuel.) Dickens seemed to use this as a class distinction. Perhaps no one actually talks like that any more, and perhaps they never did?