"You need to move your applications to be scalable and durable! The cloud is the answer" actually means "You need to move your applications into our software ecosystem, and we're pretending the hardware we use in our data centers is magical and different than yours and floats up in the sky!"
So you buy the double speak and move your applications onto their hardware and they have options available to you to do what Haus described as the "lift and shift". Your homegrown .NET applications can run just fine in their ecosystems after some initial set up pain and working with their onboarding engineers/architects. This whole time their team is talking up how much easier and faster everything is if you just migrate this code into their applications. They call it "scalable" when really all that means is these behemoths have the hardware and infrastructure in place to turn extra servers on for you whenever you give the green light with your wallet. It's immediate because it's already in place.
So you re-write your applications to use their native "microservices", APIs and SaaS products and now the problem isn't funding a new buildout in a data center that they don't own so you can suddenly call where your applications live "on prem" again. Its re-writing, probably, most of your applications almost entirely because they now exist on proprietary products you cannot migrate off their platforms in any way, shape or form. Your software is very literally fucking worthless outside of their ecosystem.
You once had an application you could package and sell to anyone, anywhere, running any OS. Now you have an application that runs on Microsoft's servers and will not work anywhere else, ever again.
This is a mild exaggeration, but that's basically the 50,000 foot view. You bought your kid a new swingset with all the hottest new add-ons, that every kid in the neighborhood has. It gets delivered and none of your tools are compatible with their proprietary screw heads, nuts and bolts. So you buy some new tools, build it, it works great so you start buying everything from that company. Now your whole house is full of gadgets and doo-dads and widgets that their tools work on! So you sell all your old tools. A few years go buy the sheen wears off the products start malfunctioning and you peel away the layers to find its all a grift. So you start fighting back with your wallet, but woops, none of your goddamn tools work on all the normie shit you want to buy.