Those numbers don't tell you that Squarespace is a pig with lipstick. It might be one! But, SAAS economics treat the ability to hit near-zero profitability as a feature of the business model, not a problem.
Here's why -- income is taxed, and growth is rewarded, heavily, in the valuation of the company. If every dollar of business you make is worth $6 (Roughly $1.2bn in revenues = $7bn buyout), and every $1 of new business you earn costs $1, then by spending all your cash, you make 5x on it. In the alternative, you can keep $0.78 / dollar, so the net gain versus keeping earnings is $4.22. I like that trade, and I'd make it as the CEO of Squarespace.
What's unusual about SAAS companies is how easy it is to manage this part of the business economics as compared to, say a bean factory. Much of the spend is digital marketing, and sales teams are much easier to scale up and down than say factories.