These were all bought pretty much when Gamecube was current gen. Over 2 or 3 years I'd say. Quite often I got them cheap (well - relatively cheap) pre-owned when people sold off their GC games. Though I only bought complete copies in very good condition - which wasn't difficult at that time. Some I snapped up off Amazon before prices got silly.
I used to have a lot more - had a complete set of the RE games, both Star Wars games, Killer 7, Eternal Darkness, Twilight Princess, Metroid Prime 1+2, Pikmin 1+2 etc but they all went as part of a big clearout I had about 5 years ago. I sold games that either I would never play (e.g. RE, Zelda) or had an update on Wii (Prime, Pikmin etc.)
I spent some time upgrading some games I had too. For example I sold any platinum editions I had and rebought the original release. I upgraded a few I had too - I'd have 2 copies and make 1 copy with the best case/manual/disc and sell what was left.
I couldn't do that now - just too expensive. My collection is smaller now but it's what I call curated. It's made up of games I'd actually play for the most part now and their condition is of a relatively high standard. Not mint but mostly very good.
I've done that with most of my collections now - Dreamcast, Saturn, PS1/2, N64, 360, SNES and MD. My collection went from over 800 titles to just under 500 and it has remained there with some buys and sales.
My recent project was upgrading my PAL N64 version to JP-NTSC by buying and selling. I did the same with Saturn...most games are now JP-NTSC but I keep a few of my favourites in PAL and have upgraded those to copies in better condition. I've started compiling a small collection of Super Famicom games in very good condition and selling their PAL SNES equivalents.
My Wii collection is quite bloated though - it could do with a trim!!