I don't think the problem is educational per se, but the level of the education.
I sort of agree (and Bored@work has a good point too).
I'm in a smaller niche than EEVBlog and only 1/20 as popular. I find the following themes work:
* Super simple that's sometimes not much more than connecting two wires together. In radio that's the old topics of Morse keys and antennas, etc even though its' been described many times before by others. Everyone needs them, they're simple and building's still cheaper than buying. In electronics it may be very basic circuits, which merges in with below.
* The old classics. Simple projects many started off as a kid. In radio it's crystal sets and regenerative receivers. In general electronics it would probably be simple 555 timer circuits, 2 transistor multivibrators and Science Fair electronics sets.
* Newish stuff that the crowd is doing (or is thinking about). Eg software defined radio in radio. Especially if it's cheaper/simpler than others and uses basic parts despite the performance trade-offs. In general electronics I'd suppose Arduino and Raspberry Pi would be in that category.
These 3 sorts of videos are timeless traffic generators - eg still popular despite being out there for 3 years or more.
There's differences between viewership and comments. 'Crazy' videos, eg destruction/abuse of electronics, tripping over, April fool spoofs get lots of comments but are only moderate in attracting long-term views. Ditto for stray dogs knocking something over and silly public comments eg talking to aliens (the local beach being a common backdrop). Although having said that these videos still attract more than more worthy educational content on circuits, etc.
It's also no secret that frequency of posting is critical (like blogs). 1 x 5 min video per week beats 1 x 20 min video per month. People are attracted to your channel and sniff around for other stuff. And there's 4 times as much exposure for advertisers so it's in their interests as well.