In fairness, acrobat is a full fledged editor of a hacked file format. My Acrobat Reader DC install is sitting st 384 MB and Sumatra is at 18.7 MB; only a factor of 20 larger. :)
Not that it justifies 2.4 GB but the products are very different. One is read only while the other is everything you could ever imagine wanting to do with a PDF. e.g. Infranview is expected to be significantly smaller than GIMP too.
For the most part that's perfect though. 99% of the time I just want to read a PDF so I just use the PDF reading tool not the PDF everything tool. That being said signing/form filling does bring me back to other solutions occasionally.