Let's think of it this way.
This is the first 'new' Metroid game in 19 years because Nintendo does not recognize Super Mario Galaxy 2 and Metroid: Other M and everything else was remakes and ports.
During te same period and not counting remakes and ports about 10 brand new Zelda games released.
Sakamoto saved you $600 by not directing a new Metroid game for 19 years.
Think Super Metroid was $60 USD back in the day, trying to search this lead me to some price charting site which declared loose Earthbound and Chrono Trigger carts are worth in the 2 and 3 hundreds of dollars respectively. Collector people are nuts.
There's the collector side of it but also the preservation side. Some of those games have broken batteries or the materials have worn out.
Finding 20 - 30 year old cartridges in good working condition is not common. Let alone with boxes and manuals. This is a bigger problem on 'newer' systems like the DS, where the cartridges break down much sooner than they did on the NES or SNES.
Pokemon collectors are panicking because Pokémon Omega Ruby & Alpha Sapphire are breaking down en masse, which are 'only' 6 year old games.
We're reaching a point where we are reaching the end of the lifespan of media not kept in optimal conditions and there is no way to fix them like you can fix consoles or handhelds.
Plus with more people playing and collecting video games than ever before the demand is high too.
It's kinda weird, I expected some games to become dirt cheap once they released digitally or remakes appeared but that hasn't really happened.
In fact, once the remaster is announced interest in the original increases too.