This is, I think, a smart move for Square. Stripe has been moving up the stack aggressively (and much faster than Square, who were very effective in the beginning, but kinda stopped innovating), making it easier and easier for people without a dedicated software team to build out an online sales channel. Weebly has a lot of that stack already built. You can build a website and sell things in a very short time with Weebly already. I imagine Square will be making the "sell things" part of it even more core to the experience.
And, businesses do not change payment processing often. If you lock them in when they're brand new and tiny and using something like Weebly, while also providing paths for growth, you'll probably keep them basically forever. We've rebuilt our website and ecommerce basically from the ground up four times since we launched the company a dozen years ago and have only changed payment providers once (maybe twice, I can't remember if we launched with Authorize.net and moved to PayPal soon after or if we switched before launch...partly based on ease of deployment and management). That's a lot of money made on that initial customer acquisition. To get businesses earlier than that, you need to have a really clear path from "I don't have a website at all" to "I have a website and can sell things with it."
Enjoy your private islands, or the next project, or whatever y'all decide to do next.