Why allow incomplete HTML block tags?

Example 107 of the spec allows constructs such as the following as HTML block openings:

<div class

What is the reasoning to allow this?
In my implementation, my regex to solve this also took care of attributes. Is that on purpose?

I guess, because that simplifies parser somehow and “nobody cares”.

That will be changed soon anyway Raw HTML blocks proposals -- comments wanted

Cool, thanks for pointing me to that proposal. That would indeed make things much simpler.