We are looking into it. To some degree, it is a resources issue. It will take a lot of time/cost to produce extensions for other browsers, and we won’t be able to recoup that cost like we can on Apple’s platforms. (Better is our only product.)
It’s also worth noting that people who already use Google products may be fighting a losing battle if they’re trying to protect themselves (and their privacy) from trackers, as our research shows that Google is one of the worse trackers across the web. (Their trackers are on ~80% of the top 1000 most popular websites.) I’ve already had experience installing the Hangouts software on my computer only to find that it tried to “phone home” constantly, even when it wasn’t being used. It was near-impossible to uninstall. I certainly wouldn’t trust them with my search and browser history!
This means it will likely also become a technical limitation in the future as Google will be working to protect the source of its income.
Still this doesn’t mean we will not try making a Chrome extension. Our intention is to try to protect as many people as possible, and for it to cost as little as possible.