Not surprising at all. Just like Seinfeld, it's an extremely popular show. It's a staple in the daily schedules of many TV stations in the US such as KTLA and WPIX (along with Seinfeld). I've seen people younger than me (I'm 24) wearing logo'd T-shirts out and about. I entirely agree with Kathi Chandler-Payatt's contentions regarding the benefits of ownership of physical media.
Streaming services these days make up a large, confusing, volatile and potentially costly world of subscriptions to vast arrays of content with examples that may be appealing to you, but also might be here one day and gone the next. Physical home video represents the perfect opportunity for the end consumer to make a one-time vote with his or her wallet in statistical support for the titles that appeal to him or her that he or she would like the right to view at will for the reasonable lifespan of the discs. There's also the advantage of Blu-ray discs (for the titles for which they are available) having superior HD picture quality and likely audio codecs than streaming services. Then there's the issue of broadband internet services (and costs) in rural areas or people living under special circumstances (such as post-secondary students living away from home on a budget).