Sierra games would not sell on todays market.
I'm guessing you don't have Wal-Marts where you live.
Examples of old games being re-released, and selling fairly well
Sega Smash Pack(20+ classic Sega games)
Need for Speed Collection(over a half-dozen different NfS games)
The Myst collections(at least the first three games, often on DVD)
Sonic Adventure:DX(over a dozen Sonic games, only one of which is 3D)
Megaman collections(not PC, some with NES level graphics)
Street Fighter collections(not PC)
Baulders Gate collections
The Sims collections XD
In other words, one game might not sell, but in a package deal, they tend to sell quite well.
P.S. Most of those collections/package deals, have been made compatible with new OSs.
Besides, do you really think modern gamers are going out and looking for free older games to play that don't really even run on their machines?
I'm going to forget about the "free" part, and go straight to retail games.
Let's look at these genres(niche market, but the higher cost of these games, helps make up for part of it), shall we?
Flight Sims(though there are many new flight sims, people are STILL buying the classics, like Falcon4.0)
Driving Sims(same as Flight Sims)
RPGs(you've never heard of Geneforge)
Besides, if you setup DOSbox to do things automaticly, there's a VERY good chance it will work, with almost no hassle.
Note
Most of these old games, are a pain to get working on new hardware/software(Geneforge2 is a new game, with VERY old style graphics).
Abadonware is like the life line for a lot of these games.
and the death of many others...
The fact that we are talking about this here is extremely hypocrtical anyway.
You're comparing someone, that spends months/years making a game, to someone that simply copies another person's months/years of work?