Native is hard relative to (the nearly thoughtless) slapping together of JS and CSS frameworks to "build" an "app." It requires paying people more and taking more time to develop.
When compared with RAD tooling like Delphi or XAML, HTML/CSS/JS is anything but easy.
- It removes the risk of spending time and money learning what turns out to be the "wrong" (i.e. an unsuccessful) platform
- It avoids splitting the effort of tooling vendors, library authors, etc. across many different platforms, reducing the amount of redundant effort spent reimplementing things in platform Y that already exist in platform X and freeing them up to work on unique ideas instead
- It brings the largest possible number of people underneath one umbrella, which makes that community more economically attractive and therefore increases the number and quality of tools and services they have access to
Not that it's all sunshine and roses, of course, but it's not without advantages.
People who have never heard of specificity or modularity start writing code that will run on thousands of browsers, and in turn those users experience a slower web.
The other side of that mess is when developers with more experience thoroughly plan out the architecture of the web app, to ensure it operates on a performance budget and the user experience stays positive. Just as native apps, this also requires paying people more and taking more time to develop.
Having helped many organizations understand how to build JavaScript applications across a bunch of different platforms, from my experience what they are trying to do is improve their ability to iterate and remain responsive to user needs across all the devices users want to interact with.
As a user, I expect and prioritize applications and experiences that are available to me wherever I choose to use the service. Web stack tech is facilitating this.