Your work history doesn’t show up in comments, but a headline that includes “ex-google, ex-fb, etc” will easily show a wide audience that you’ve worked at top tier companies when you comment or show up in a connections list. It’s an easily way to gain credibility without someone needing to view a your profile/work history.
Some people like to be socially engaged on LinkedIn and are proud of their accomplishments. I’m not sure I fault them for enjoying any positive attention they may receive from their previous hard work. I also think social networks benefit from individuals that are highly accomplished and contribute content on the platform.