Because that's the standard. Have a look at the other katas on the site, or look at the names of in-built JavaScript functions:

isInfinite, parseInt, lastIndexOf, copyWithin, toLocaleLowerCase, etcEtcEtc

...and yes, style guides: Google, jQuery, W3Schools

To explain from the opposite direction, look at these in-built PHP functions:

• htmlentities, html_entity_decode, strchr, str_pad, gettype, get_class, is_numeric, isset (inconsistent underscore usage)
• strtolower, deg2rad, strtotime, ip2long (inconsistent use of 2/to)
• file_get_contents, fwrite (inconsistent abbreviations)

It's unnecessarily difficult to remember the names, because there's no consistency.

Really dude?

Why?

Why it should be camelCase? Don't say "js style guide". Just say why it should be?

Not a question.

The function name should be in camelCase.

The link in the description should not lead to the trainer.