why does it need (guessing here) 4 days of studio time and loads of crew to record a good song.
If you want a detailed answer to that, you're on the wrong forum. But by way of illustration, I recently worked with a band who were contributing a track, along with a lot of other bands, to a charity CD. Bands, studios, engineers etc. all gave their time free (so you might guess that no-one was wanting to spend more time than necessary on the project!)
I worked on the first session - the track lasted about 5 minutes, and the drummer got it right on the third take. (Which on its own is pretty amazing, since even seasoned session musicians make mistakes, and often need multiple takes which are pieced together to get one good one). 15 minutes then to get the drums down? Yes - but only after we had spent about an hour and a half moving mics, retuning drums, trying different damping methods on the kick drum etc. to get the drum sound the band wanted on the track. (And that's pretty quick). And before we could even start to do the drum takes, we needed to record a guide track - the whole song with a rough mix of keyboards, drum machine, and vocals which the drummer then used to play along to. So from unloading the band's gear in the studio to getting the good take of the drums used up the entire morning. In the afternoon we added the bass track - it was quite a complex track, and the guy never got it completly right once, so we had to make sure each section of the track was available on at least one take. We recorded a few different versions of it so that we had choices at mixdown time. That was it - first day gone!
Someone else took on the second session, but I know from talking to him that day two was similar - multiple versions of two guitar tracks, keyboards, piano - all recorded individually, and all with multiple retakes. Working late into the night they got the vocals put down.
Day three, the band cleared, and left it to the mixdown engineer who spent a full day listening to all the different takes, piecing together the best ones, and mixing the whole song together. After he had completed his mixdown, it went to someone else for mastering, which is yet another time consuming process.
Having worked on plenty of commercial recordings, I can tell you that this was a pretty quick turnaround time, and a lot less than is spent on many tracks.
A&r people out looking?? There are plently of bands screaming to be heard now,
Yes, and plenty of them are very good - but without the backing of a label, most of them will never have any commercial success - that's starting to change, but it's a gradual process. And for every good band out there, there are an awful lot of rubbish bands. Even among the good ones, you often find that they can "pull it off" onstage, but are hopeless in a studio.
and because they dont get picked up on by these a&r people, they loose out?
Basically yes! You've got a choice if you want to make it in the music industry - either you try to get picked up by a label (And put up with the fact that until you become a household name, they will make more money out of you than you get yourself!), or you go it alone. Go it alone is becoming easier, but it's still a hard slog, and quite often depends on getting a lucky break. Many brilliant musicians don't have the business skills and experience to promote themselves, even if they had the technically ability to put together a good recording on their own. (Good recording gear is now relatively cheap - but you still need to know what you're doing with it to produce a winning track!)
shutter - can I join your company? First preference is for Getaway Car Driver, but if that position is gone, I'm really good with a tea trolley!

I'm not convinced that deterants don't work - I really do slow down to 30mph now where my mate got 3 points!

And I don't take drugs for athletics anymore (actually I find that the picture on my TV is just as good without them!)