You could say the same about Coke vs Pepsi, but that doesn't stop either one from trying to maximize their market share.

I think the dev tools in Firefox and Chrome are much more distinct from each other than Coke vs Pepsi, though. The last time I used the FF dev tools (which was admittedly over a year ago) they were much slower and their support for changing attributes on HTML tags inline was more limited. I think the Net tab had fewer features too but this is going back a while so my memory is fuzzy.

Even if the only difference is personal preference, what's wrong with Firefox trying to accommodate more users' preferences?