Growth of prediction markets over time?

This would be extremely annoying to gather, way more effort than the value of information would warrant. Nonetheless, here is a database of prediction markets which you could use to get started. 

Things that make this annoying:

• Presidential betting markets were fairly big before the, say, 1930s
• A large part of the volume comes from sports betting, and I imagine that you don't particularly care about it, but disambiguating by type of market might be difficult
• Prediction market popularity waxes and wanes, so you'd have to get data for a lot of different prediction markets, some of which may not exist any more (e.g., Intrade) or which lose market share over time (e.g., Iowa Electronic Futures)

Some simplifications:

• You might want to look only at US prediction markets from 2014-present, and only look at the top most popular ones (Nadex, PredictIt, Augur, Polymarket, Kalshi)
  • For all I know, Nadex might just completely dominate total volume except maybe during US elections.
    • I'm counting Nadex because of the economic indicators (e.g, unemployment). If you also count things like shorting Tesla as a prediction-market-like, things would also look different.
• You might want to look only at PredictIt
• You might want to just ask somebody who has been playing prediction markets since 2014 in the US for their subjective impression.