The curious thing is that they don't pay the photographers. So that kills the stock photo business model for everyone else. You can't take nice pictures and expect that some day someone will pay you for the un-watermarked versions now UnSplash has taken that market away.
So money is now going to these CDN hosts and other software suppliers, spent like water with a business plan that is not in the article. I guess the likes of Adobe can bung them a few million a year as the service is worth that to them. Same with Squarespace, they can partner and pay a few million to keep unSplash's lights on.
So this has some interesting negative effects from local communities where people once had their own websites and their own local photography businesses. Although unSplash might not directly be reaming out every small town in the world making it impossible for anyone to make a living from stock photography, Squarespace kind of are. Web pages have made themselves complicated today, once you needed Notepad and an FTP program, nowadays you need a team of developers to spend months in order to put 'hello world' online. So people are nowadays going with Squarespace and other highly marketed services, that, in turn, rely on UnSplash.
The images initially look very impressive with UnSplash but I was once really impressed by a Pret A Manger cafe. Then I realised there were many Pret A Manger cafes in many towns and they all were the same inside. Quality stuff but identikit. At the same time, each outlet was not exactly identical, there could be a different amount of chairs, the counters could be laid out differently. (Readers outside the UK could swap Starbucks for Pret a Manger).
I see UnSplash as a photo version of a Pret a Manger cafe. After a while the images are all very much the same. This is good and it is bad. It is bad in that so much of the internet becomes predictable and generic. It is good in that it becomes quite easy to do better. Much like how you can do better than Pret a Manger at making a sandwich, just by making your own, so it is with UnSplash, you can get far better photos for your project by taking your own photos and doing your own editing.
I would not bet against the success of UnSplash any more than I would bet against the success of Pret A Manger. However, I will be making my own bread or visiting independent cafes, oh, and taking my own photos rather than using 'free' formulaic stock photos.
Enough of the analogies, a critique of UnSplash and what they are not doing. If you look at a Squarespace site that has some UnSplash banner then the image will be several thousand pixels by several thousand pixels. This is good but bad. Good in that native phone camera resolution images are nice to see, bad for bandwidth.
This bandwidth is mitigated by CDNs. The CDNs do the different resolutions but it is quite dated tech being used to do this. I think that for most website owners, e.g. one's small business, there is a performance benefit in using one's own hosting and running Google Pagespeed to optimise and serve the images. This can work with the low bandwidth browser flag and do responsive source sets.
This means putting the original image dimensions in the HTML for Pagespeed to write out the srcset images, putting in a picture element and so forth. The images also get sent as webp when needed.
Now if I did want to show some thousand pixel images then I would want to do that with OpenSeadragon. This takes the deep zoom aspect to a whole new level. It works fine for a small website without a complex CDN.
Now there is no reason why I could not 'steal' a few UnSplash images and serve them my own special way with Google Pagespeed doing all the work on my own server but I am not going to be running generic stock photos anyway.
Google's Pagespeed falls in between the gaps between large compartmentised teams so nobody is using it. Why would you when for the same reasons as nobody ever got fired for buying IBM, nobody gets fired for spending a fortune on a CDN? However, if Squarespace and other UnSplash clients decide they can actually offer a better, faster product due to improved tech for serving images then they can start doing their own stock photography.