Why are stocks taken off the stock market when ...

Because they are no more liquid. And no body will prefer buying those stocks as also the movement gets slow and their chances of price rise are rare.

I have no idea what "stevenc" is saying in his response to you.  Each stock listing service (American, Nasdaq, Over the Counter) has their own requirements for a company to be listed on their exchange.  If the book value of a company's stock falls below, say $1, they can be delisted from that exchange, forcing them into a "penny stock" limbo.  I think General Motors recently had that problem, with the value of their stock plummeting drastically. They may have been dropped from the Dow Jones list of powerhouse companies.  That's why it's such a big deal when a company gets listed on the New York Stock Exchange. Frequently you see the company bigwigs happily pounding the gavel and ringing the bell over the trading room floor on Wall Street.  They may be celebrating their acceptance onto the publicly traded stock listings.  It gives their stock exposure and a place where investors can follow their value, often helping to raise the price.  On the other hand, once your company's book value drops below the magic number, you can be delisted.  Now that stock is mixed in with "has beens", "wanna be's", and small start ups.

Because of the Exchange's rules, for instance the second largest exchange in the U.S. requires that a stock maintain at least a $1 value over a three month period and make all filings.  If it does not, then it goes to the "pink sheets."  The "pink sheets" are for companies that are not in compliance, less than $1.00 in value per share, small start-ups, or stocks that do not trade often.