I voted to close this question, and I stand by that.
Firstly: I disagree with the Google statistics provided.
I found that "key thob" comes up less than 0.1% of the times that "key fob" does:
That Google auto corercts thob to fob is not significant - it does the same for dob
and "key dob" gets more hits than "key thob".
Is that a significant term?
I admit that these stats could be regional – I am using Google in the UK.
Secondly: if one trys to look up key thob in an online or paper resource, then one finds that it does not exists as a term.
Thirdly: differing pronunciation is rife within English. This is not remarkable. Take, for example, how most Londoners pronounce thief as feef. I even know some people who over correct the typical th- to f- mispronunciation and end up substituting th- for f- (e.g. fewer -> thewer, fifth -> thith, etc.).
I do not see merit in a question that asks "why do I mispronounce this word?" when it is only them and a scant few others who do it. The answer won't help the internet at large, or them particularly.