There are many reasons, most, if not all already specified.
1: Shmups, by nature, are generally harder than other games
2: Non-localized Japanese games, by nature, are generally harder than non-Japanese games
3: Doujin games, tend to be harder than non-doujin games. I like to think of it because doujin producers KNOW that only hardcore gamers and niche fans buy their products, and everyone knows hardcore gamers hate how easy most games are in this day and age.
About Touhou being easy compared to every other shmup, I've said it before and I'll say it again. The danmaku dodging in it is NOT much easier IMO, it's just the super generous extend count+bomb count+deathbomb timer, powerup supply, etc makes it easier. I rekon someone who can beat any cave shmup with a few deaths still has a few deaths in a Touhou game (on lunatic) as well. Honestly if you dislike a game simply because it says "game over" 6 deaths later than another game which does after 3, you seriously need help. >=P...Though I still think the stages (non boss portions) themselves are pretty easy for the most part.
about #3, I think that the doujin shmup developers like the genre, and would try to make something that they like, rather than try to make them more difficult than arcade shmups. ZUN himself has said that there's freedom into the doujin scene, to make games without worrying too much about how well your game will sell, or something like this.
about Touhou being easy compared to every other shmup.. there are easier shmups too :p
The difficulty, while subjective, doesn't reside in Touhou being a bullet-hell. There are complaints from shmup players about this series, not all of them are about Touhou being easy but about things such as the gameplay (unremarkable stages, bosses taking most of the stages' play time, less need to move around the screen rather than dodging some few pixels and watch bullets
fly by your side, slow bullets for the most part -- it would be difficult for arcade shmups to have pretty patterns with fast bullets, and pretty patterns don't necessarily mean effective ones or fun ones to dodge through. Personally, I enjoy scoring more on other games.)
>> I rekon someone who can beat any cave shmup with a few deaths still has a few deaths in a Touhou game (on lunatic) as well.
any info about this guy? I think that, when learning a new game ( such as playing Touhou for the first times to learn it ), dying is part of the learning process, not everything in Touhou is reaction-based (and that applies to arcade shmups as well). The notion that dying in Touhou means that the game/series is difficult is.. relative.
>> Honestly if you dislike a game simply because it says "game over" 6 deaths later than another game which does after 3, you seriously need help. >=P
personally I don't enjoy grazing, especially in Touhou
(however there are few moments where I do, in Shikigami no Shiro 3 and Raiden Fighters Jet, because I'm not required to dodge as many bullets as possible). I don't enjoy MoF much, too, because the faith counter will often drop, and that will frustrate me ( even if I don't die ) because I tried to play MoF by using my instinct, rather than memorization.
I do like HRtP, LLS and PoFV (and PoDD, too), though. May enjoy MS if I learn its scoring system, too.
>> ...Though I still think the stages (non boss portions) themselves are pretty easy for the most part.
I just wish that I could memorize Touhou stages as well as in arcade shmups.. as I believe I've said elsewhere, the enemies aren't diverse enough in Touhou, and the background can't be used as a reference to help you remember what to do in advance. ( also, my execution isn't precise enough )