That is certainly one way to look at it. I'll propose another way to see it: There are always trade offs. For example, you could hire enough people to simultaneously work on a Mac OS version, a Windows version, an iOS version, an Android version and a web version of your product. Of course this is going to cost a lot of money and this cost will be passed on to the users. If the users prefer the subtle differences between the UI in platforms so much that they would prefer to pay more for a product than that would be an advantage. Otherwise that is a disadvantage. Potentially a really big disadvantage. There is also a case to be made that some people would definitely want the product to work the same in the web browser as it does on their desktop. Slack is a good example of this. I don't want to learn a new user experience for the moments when I'm on another machine without Slack installed and I just want to respond to a comment quickly, I'm very happy the web experience and the desktop experience are similar.

Making absolute statements about why people make certain choices or believing them can definitely lead to false conclusions. People don't only use cross platform toolkits because they do not want to do work. Sometimes it is the best solution given the features and constraints. I like to think of it as being pragmatic.