Metapod Raid Boss
Why, Just Why. Who is going to waste a Raid Pass on Metapod, when there is Legendary Raids all over the place. (What Doesn't Kill You Makes You Harden)
Answers
Do you remember the recent event that gave bonus XP for new additions to the pokedex?
After that, I imagine Niantic looked at what is missing from peoples dex and added them to the raid rotation.
Sometimes, updates aren't all about the hardcore players....casuals pay good money to play when they aren't busy doing other things.
You answered your own question. Someone who can't beat a Legendary raid, can't take down a level 3 or level 2 by themselves, and struggle with most level 1 raids. In other words, a beginning player. They can participate in raids, use their free daily pass, and get 3000 XP, which is a LOT for a beginning player.
And the phrase is "What doesn't kill you makes you stronger." Your version is, well, kind of sexual in nature.
Unless you intended that, which makes no sense given the rest of the context.
Same reason why Caterpie nests are sometimes in rotation, Caterpie are nowhere near as common as any of the other trash pokes and newer players may need the candy for a Butterfree (and don't want to waste their rare candies or have a caterpie take their buddy slot).
Is it a lame raid? Absolutely, but Tier 1 raids are for exceedingly easy bosses that are mons that have candy people may need.
Additionally, since the raids have shifted, but not completely been replaced, and we are likely to get Gen 3 soonish, it's probable that the raid bosses will shift much more often, so players have the opportunity to get candy for many different mons. Also why even the higher tier raids now have very lackluster mons that may not be very common in the wild. Even the Magmar and Electabuzz raids fell into this category under the previous set.
When was the last time you saw a caterpie in the wild? They are pretty rare these days, with spinarak being the most common bug in addition to weedle. Caterpies used to be annoying to get out of 2 km eggs, but they are no longer in the mix. With the generation 3 dustox/beautifly iterations coming, caterpie will be even more rare.
If you have played since the start, metapod isn't a big deal. But, as someone said, if you started the game when the raid system started, you might have had trouble accumulating 72 caterpie candies to evolve a butterfree.
I expect we're gonna see the gen 1's rotated pretty regularly since the full gen 3 release is just around the corner. These mons will become less common when gen 3 does come & raids will be a good place for new starters to find the ones they need. Level 1 & 2 raids are not for high level players so they shouldn't be upset by mons like metapod appearing. Making the game playable for newbies while managing the sheer number of different mons in the game is a challenge for Niantic going forward. The new level 4 raids tho are, ahem, questionable at best & won't be getting many higher level players excited.