The high velocity web tech landscape and a startup (velocity) mentality are more likely the reasons why this was not made originally (most likely a good trade off, in particular the startup velocity argument). I'm a little surprised a community like HN don't see this, and rather bash Electron being the devil of all things (as some comments seem to imply). We should rather commend Slack for (obviously) making a decent tech choice (using a perspective where what really matters to them; rapid growth, is/was the first priority above all else, including "technical excellence").

I mean, it's not that a C++ application wouldn't need a rearchitecting for startup performance, but it would likely not be needed for an application as simple as Slack.

I see Slack as an incredibly full-featured app. As always, many people might not use all the features, but that doesn't mean that nobody does…

I'm not saying Slack is not full-featured, but it's definitely not on the same scale as some of these other applications.

Or, more simply: Slack (and other similar products) are not just “chat applications”.

That's the modus operandi of many unpleasant things like bacteria or cancer cells, why should it be commendable on its own?

I don't know if the total amount of work over time sums to approach that of a portfolio of native apps, but even if that's the case, there's a world of difference between spending extra time improving a product that's already out in the world and developing the first cut.