Because a company feels there is money to be made by offering a simpler solution to interested customers.
Does every product really need a technical justification? If every person at your company is comfortable setting up email clients, IRC bots, and bouncers, then this isn't a product for you.
If you would rather just pay someone $2/person/month to set this up for you, then this is the product for you.
It needs some kind of justification, otherwise it will die. HipChat being offered for free may extend it's life, but I still don't see a point. Everyone has access to GChat, so 99% of the problems are already solved. The dev shops would probably rather use IRC especially since the experience for power users is so terrible. That does not leave room for HipChat in this world.
My company just moved from a GChat-centric XMPP system to an all-in HipChat system. We don't have Google Apps because we have our own Exchange server, so not everyone gets a sane email address that can also be used as their GChat handle, so we've all relegated to using personal or work-specific personal Gmail accounts.
Just last week we onboarded a new developer and instead of having to spread her personal GChat address all over the company and make sure that everyone has authorized her to speak to them, and worked out the kinks for the few (like me) who run their own XMPP server that play russian roulette on whether Google is going to allow federation today... we just sent her a link to a URL which allowed her to create a user and immediately started downloading a client that once authenticated, connected her to the entire company.
Granted, we could have used our internal IRC server (we actually do have one set up), but the maintenance behind it really started to get to us. In order to use it we had to VPN in and connect, and backlog wasn't available to people that aren't technical enough to understand shell clients (like our project managers). When we did decide to open up the security permissions we had spam bots connecting 24/7 trying to get into our channel, which we then had to password protect, which ended up being another piece of tribal knowledge that "you just had to know".
Still, I continue to have Campfire (Flint.app), HipChat, Adium with XMPP for OTR, Google Hangouts for multi-person conferencing, Email, irssi and Twitter open all day. I wish I could consolodate them all into one, but I can't because they all have specific use cases. If HipChat was to allow an OTR plugin and multi-person video chats and screen sharing, that'd get rid of 4 of my communications^W daily distractions, but it wouldn't get rid of all of them because they serve different purposes.
At the very least, HipChat being free is a much better argument against using Lync now.
Does every product really need a technical justification? If every person at your company is comfortable setting up email clients, IRC bots, and bouncers, then this isn't a product for you.
If you would rather just pay someone $2/person/month to set this up for you, then this is the product for you.