I collect coins and I think the description of the hobby (and its putative death) isn't quite right.
1. Rare coins are in fact hard to find, even in today's internet world. They are usually sold in auctions, which might happen online, but still not that frequently. It's not unusual for examples some specific rare coin to be sold only once every few years. If the coin is also obscure, it may not be prohibitively expensive, so this kind of situation isn't the sole province of rich people.
2. One area of collecting is to get all the rare items. Another is to get all the minor varieties of a common item. These varieties may not be very rare, but it still takes a lot of effort to be able to distinguish them and to find them. Some collectors will obtain large numbers of relatively common coins and sort through and scrutinize them to try to identify interesting varieties.
3. An important part of collecting is getting good deals. This is surely a lot harder than it used to be because sellers can more easily figure out what things are worth and you won't find something grossly underpriced in a random antique store as often these days. But filtering through buckets (or online listings) of large numbers of coins can still be fun and lead to spotting good deals.
So I think there is room in the hobby for nerd-like behavior (per your definition). I would argue the decline of the hobby is more due to competition from other similar hobbies (a generation ago you could collect stamps, coins, baseball cards, or rare books/comics - now you can collect beanie babies, Pokemon cards, NFTs, funko pops, action figures, etc.). I think stamps have suffered more than coins because stamp collecting has more of an aesthetic component (which has faced stronger competition) while coins have a historical element that is less well replicated by collecting newer things. This difference isn't obvious in the google trends graphs you posted but I believe is observable from looking at prices of stamps vs coins.
I collect coins and I think the description of the hobby (and its putative death) isn't quite right.
1. Rare coins are in fact hard to find, even in today's internet world. They are usually sold in auctions, which might happen online, but still not that frequently. It's not unusual for examples some specific rare coin to be sold only once every few years. If the coin is also obscure, it may not be prohibitively expensive, so this kind of situation isn't the sole province of rich people.
2. One area of collecting is to get all the rare items. Another is to get all the minor varieties of a common item. These varieties may not be very rare, but it still takes a lot of effort to be able to distinguish them and to find them. Some collectors will obtain large numbers of relatively common coins and sort through and scrutinize them to try to identify interesting varieties.
3. An important part of collecting is getting good deals. This is surely a lot harder than it used to be because sellers can more easily figure out what things are worth and you won't find something grossly underpriced in a random antique store as often these days. But filtering through buckets (or online listings) of large numbers of coins can still be fun and lead to spotting good deals.
So I think there is room in the hobby for nerd-like behavior (per your definition). I would argue the decline of the hobby is more due to competition from other similar hobbies (a generation ago you could collect stamps, coins, baseball cards, or rare books/comics - now you can collect beanie babies, Pokemon cards, NFTs, funko pops, action figures, etc.). I think stamps have suffered more than coins because stamp collecting has more of an aesthetic component (which has faced stronger competition) while coins have a historical element that is less well replicated by collecting newer things. This difference isn't obvious in the google trends graphs you posted but I believe is observable from looking at prices of stamps vs coins.