So you'll target a system that gives you the best chance for success and the best chance of high sales.
Xboxone sales: 6 million, ps4 sales 9 million, roughly.
PC's with steam : 75 million
Ps2 is the greatest selling console *ever*, at 120 million units sold, (sold, not active...most of the old units are either dead or not in use, the sales mark was reached just 3 years ago, after which production was stopped).
So the largest market is undoubtedly the PC.
When you have a relatively powerful system that is owned by millions and is exactly the same hardware setup for those millions you are going to target them first. With PC development you have so many combinations of setups to contend with you have a whole room of test rigs and you still risk a f-up when released.
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The problem was big during the 90's when there were a huge number of devices and no easy common interface that one could use, but even then the PC was not abandoned.
This was because the PC could do things consoles couldn't, be it raw power, controls and censorship from publishers and just the nature of the market(more mature). Even when games like quake,diablo and starcraft were released for the consoles, they were really bad watered down versions of the original game).
In fact if you think about, the pc market was actually smaller in the 80's to the mid 90's and has grown over the years, while that of consoles has shrunk, There was a time when PC's were considered bad for games, and that it could not produce high quality graphics like mario.
(till carmack came along)
Anyway the problem has been mitigated due to freely available engines that do a lot of the lifting in terms of tech. and these are already tested extensively by middleware makers. Most games made today (either console or pc) are built using some engine (say source or unreal engine, or maybe apis like xna), and it's very easy to make a pc build.
Besides, if it was so much trouble, people would not be investing cash to create PC versions of console games like devil may cry.
If you think about all the big selling games on the PCs they are created using already existing engines (like garys mod, counter strike) or even better, using custom maps (in the case of mobas, initially atleast).
The entire minecraft engine was done by a guy in his bedroom, and became one of the best selling games, and was primarily a pc game, not many technical difficulties there.
A bigger reason for the slight dip amongst publishers was piracy more than anything else. The biggest issue was the over pricing of games and the spread of broadband connections which encouraged people to pirate stuff. This resulted in stuff like root kits, or people delaying release of their games on the PC platform.Piracy again has been reduced a lot due to aggressive pricing on stores and f2p models.
The other reason was big console companies holding off release of games to other platforms by paying big cash and keeping things exclusive. That was a strategy that didnt really work, and most companies prefer to launch to all major platforms.
Of course if you have something that doesn't need crazy hardware things are different.
Yup this is actually important along with the lowering of price, the lowering of tech requirements. People have now realized that you can make nice looking games that can run on 6-7 year old PCs, as the performance is sufficient, the focus now is on gameplay, immersion and art style over tech backed realism.
Consoles are sort of a niche market now, as hardcore players would prefer the PC, be it, either mobas or fps's or rts (e-sports!), or even quirky indie games. The super casuals would go on to mobiles and tablets, and would get their gaming fix from there/
