According to the HTML specification multiple white spaces has to be ignored if not inside a
PRE
block:
In particular, user agents should collapse input white space sequences when producing output inter-word space.
The Qt implementation just follows the standard.
Open your HTML file with a browser and you will see that it is rendered in the same way.
If you need a different rendering with multiple spaces, you have to format your HTML input accordingly (e.g. by using
non-breaking spaces or
PRE
blocks).