Just from a logistics perspective hardware is harder than software to make profitable, and robots as a business involves a lot of hardware. More things have to go right, fewer things have to go wrong, etc. You rely on an entire supply chain to get things mostly right mostly on time, and that supply chain is mostly out of your control; you can have strong contracts, you can line up multiple suppliers for each part, you can vet them carefully, but at the end of the day you're tossing the dice that they'll deliver.

I've been working with a robotics startup for the past few months, and I'm often struck by how much extra stuff has to come together to deliver the product (in our case, we have to integrate with phone and elevator systems, have to deal with various regulatory compliance in every country we ship to, etc.). The sales pipeline is also long and expensive, involving shipping out multi-thousand dollar devices for evaluations, sending people out to demo the devices, etc. It's a production involving a half dozen people and thousands of dollars worth of resources to make every single sale.

So, yes, I think they are harder than some kinds of businesses. At least an order of magnitude harder than software. Though, because of it, the competitive landscape is somewhat smaller...robots are cool, so a lot of people want to work on them, so there's more than the market will support, but it's less pronounced than, say, the mobile app market in terms of competition for customers.