Looking at the various comments in this thread...

Filesizes for most fanfic (and other text) are nothing compared to sim download files, and yes, that does make a difference in hosting issues.

Also fanfic is a heck of a lot easier to deliver, you don't need to explain to people how to read it  (whereas in the sim community people expect support when they can't figure out how to put the stuff in their game).  I am sure with fanfic you can also get rude people and hate mail and such.

'Unlimited' hosting is not.  No matter what they claim, and they always have limits, sites that outgrow their 'unlimited' hosting find that pages cease to load correctly, downloads fail, etc.  Most of those sites plan to host -your site- and many others all on one server, assuming none of them actually need the whole server. 

MTS2 for instance, has a farm of servers, I don't have it memorized, but it's something like 7-9 servers, and at one point our monthly bills were around 2k...  Now - MTS2 has managed to keep the content free, but has had to sometimes run fund drives in order to keep things going (and we've had mixed results with ad services to generate revenue).  Even with that, we've had periods when people were having problems getting to the site or downloading.

I'm involved with a facebook app - lil greenpatch - which quite outgrew it's hosting at AbigcompanyIwontname.  Pages stopped loading, the database overloaded, coding changes did not help, and they simply said, sorry, no, this is all we can do for you.  GP had to locate hosting at a service designed for high volume sites.  With 500,000 daily users, even -without- large download files, the other company's system (and they did add servers) was just not able to handle it.

Bigger sites also often end up using databases (forums use a database too). Often forum software is not optimized for high volume - so they you need a great programmer (like Delphy) or you might need to hire a consultant to come in to help fix things... or buy more servers and hope that helps enough.

And historically - why most small sites offered 'donation gifts' is because (and I've been in this community since sims 1) -- because shockingly enough, most people were not motivated to even throw $5 at a site they liked if they didn't get something extra back. 

There are two ways to look at the sims downloads

1) as a consumer - who bought the product and is now 'shopping around' online grabbing more things for it.  The people who come at it as a consumer will gladly take things that are free and -not- pay, even if the site owner doesn't want to spend hundreds a month out of their own pocket funding this 'hobby' of theirs.  (and frankly for how some of these 'free' customers behave - hassling those who offer their work free - sometimes yes, it is a wonder that more people don't quit.)   At any rate, those coming at it from a 'consumer' point of view aren't going to 'donate' when they already got the stuff for free, but might 'buy' a donation gift.

2) as a member of a community - someone who sees themselves as a member of the community, even if they never create, and only download - those people might realize that there's more involved and that just because someone has talent and time, that doesn't mean they can afford to pay for hosting once it's gotten beyond the $10-$20 a month level.  Those people might donate from time to time to their favorite sites without having to be bribed with 'thank you' gifts.

Anyway - the sims world is NOT a community really.  It's a bunch of people with a common interest, and while some of the folks congregate on boards and form communities, it's not all one big happy family... There's as many people hating on each other and criticizing for one thing or another as there are any that are supportive... if not more.   But it is people who will behave as a community and be supportive of the others in it that make 'free' sites possible... because once a site becomes popular, hosting becomes difficult.

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Anyway, my 2c, with experience running big sites (and I remember when 10k visitors a day made us one of the top 10 sites on the web, lol).  There's a lot more involved that people who haven't been involved with a very large site don't realize.

PS - I've seen more responses since I wrote this - and indeed for a little 1 creator site that -hasn't- hit it big, they should just treat it like the hobby that it is, and not expect that people need to pitch in to pay for the $10-$20 a month of hosting.