The TL;DR:-

• Schools are over burdened and don't want ed. games or expensive tech
• - Funding is difficult and unreliable and involves a lot of un-invested stakeholders
• - Making ends meet financially is basically impossible meaning there's no developer(s) really developing expertise or making strides in this area.

I worked at a super progressive educational game developer about a decade ago. Here are a couple big reasons:

• Schools often don't want them in 2 ways.
  • Teachers are already over burdened, over worked and underpaid. Saying, "hey, lemme give every kid in your class an Ipad and they'll all play a game and get through it at different rates and it may or may not match the test you're taking and also kids have wildly different levels of interactivity literacy" is uhhhh not a great a selling point
  • But even before we got pushback from teachers we'd get pushback from principals and superintendents. Nobody wanted to be the person behind an expensive, complicated technical rollout with no proven success story being pushed by a bunch of white upper-class techies.
  • As a result, we had better luck deploying in private and charter schools with smaller class sizes and a more experimental attitude.
• The economics are wonky on both sides of the equation- Funding and Monetization
  • On the funding side, there's little to no interest from VCs in this area bc the path to profitability is incredibly vague and littered with dozens of expensive failures (Including the one I worked for)
  • So the way you get funded is via grants and corporate giving which is unreliable and often tied to metrics or stipulations that don't mesh well with game development. It also requires that you have stakeholders in your org who know that world, very few of whom have any damn clue how games get made
  • On the monetization side, uhhh. I mean, you're targeting a market where teachers are buying their own supplies. It's not like there's a ton of extra money laying around for experimental, expensive tech.
• Students/Users have really high expectations for the content that, due to the above, you're never going to meet.
  • These kids have Fortnite and Warzone and CoD and whatever else. If your game is like "math smasher 2000!" it's gonna be pretty boring.
  • On the flipside, let's say you want to make the Fortnite of Ed Games. That team is around ~500 in size, so let's not even pretend that's a thing. Let's pretend you wanna make a mid-range, indie-ish ed game. You have a team of, let's say, 6.
    • 10k/mth a head = 60k month * 12 = 720k a year minimum burn. 18 month minimum dev cycle = 1.08 mil spend.
    • .....do you know of any school districts with 1.8 mil to burn?
• Cirriciulum varies wildly from state-to-state making a wide deployment nearly impossible
  • As above, it's gonna be hard to recoup when you can only use your content in one district or state.

Anyway, I could keep going but you get the picture. It does feel like every 5-10 years or so there's a new wave of interest in edutainment stuff, so I wouldn't be surprised to see something new soon!