Why Do Web Space providers provide web space for free - ?

I have checked many sites that provide free web space . Are they genuine with their service , especially the ones that do not post forced Ads on their customers' websites ? I mean do they resort to some fraud means like diverting traffic from your website to theirs etc.
Which FREE web space providers are suggested that allow Ads on their page ?? since I am just beginning .
Also tell how much web space is required to build a 5-6 page average website and what are the technical services I should look forward to .
Suggest any freeware website monitoring tools especially traffic and uptime monitoring . Can I use them with my free web space provider ?
Please answer only with relevant information .
Thanx a lot in advance .!!!!

They get alot of money from advirtisment, the more visits to the site, the more the site makes....

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