Dota is kind of fun to watch even if you're not that well-educated, but the announcing/casting style needs a serious overhaul, and general popularity needs a lot of "support" from good production: information overlays, slow-motion replays, giving casters the ability to zoom out to a full-map view and draw arrows, etc.
Look at hockey, American football, and road cycling for examples of complicated sports that are somewhat hard to understand without prior knowledge, and people really enjoy watching those, too.
At one time DotA2 had a noob friendly stream that would explain what was going on in greater detail, but it's a hard balancing act. DotA2 allows in game spectating which actually means you can click in items to figure out what they do. It would be cool if streaming platforms had embedded item and hero information for users to be able to expand on demand.
Complexity is something that affects League and DotA2. It's hard to know what all the things on screen even mean, and why they're important.
Look at hockey, American football, and road cycling for examples of complicated sports that are somewhat hard to understand without prior knowledge, and people really enjoy watching those, too.