You're making the mistake of thinking that everything is just a technical challenge that you can throw money at, and that technical superiority is the only trade-off.

Just because an enterprise has funding doesn't mean it's wealthy in other, more scarce things like organizational capital. In fact, I wouldn't be surprised if all the client developers at Slack would love to split off into dedicated platform teams and do a rewrite. We as developers love that shit.

But you should try to understand why these enterprises make these trade-offs and why they are still in these positions in spite of how much disposable money you think they have.