Instead they just tell them to buy and than sit there and watch their clients lose all of their money?

idk

it is illegal if they reveal ahead of time and sell stock before it plumets

Often it is because the broker will lose money if you sell.

Read this:

http://saveyournestegg.com/scam.html

And, if your broker is calling himself a 'financial advisor' (95% of financial advisors are brokers/salesmen, then you should be in a well diversified portfolio that you understand and should not be freaking out about.

Selling short is an incredibly risky move; you have a limited potential for gain and an unlimited potential for loss. (The opposite of buy & hold).

It is not appropriate for non-professionals. Buying put options or placing limit orders is a reasonable choice for clients who understand the market well enough to limit downside risk ''professionally.''

professionals & experienced traders short stocks all the time, in good markets & bad. The problem with retail brokers is that a novice speculator can easily lose a fortune selling short . when u buy a stock the worst that can happen is u lose ur investment. when u short a stock, there is theoretically no limit to how much u can lose. Most retail clients get screwed enough by following broker is advice, urging them to short would make things worse & invite regulatory action. .. & retail brokers have historically been very reluctant to even rate a stock as a 'sell', much less a 'short'. When analysts publically advocate shorting a stock, companies will stop talking to them & conventional sources of information dry up.

the first 3 above are from idiots
the reason brokers never tell their clients to sell short
is because they are dipsticks
they do not know their heads from their ***

Most prudent stock brokers would advise their clients to short when the markets r against their clients' holding positions especially when the markets' fundamentals r not in their favor in a longer term. For the old school thought, people r talking about investing but nowadays due to tremendous market forces interplay thus information become very speculatively . Brokers r human beings where they r also temperamental in their behaviors in believing & holding on the facts that nothing has changed, & that tomorrow the market would turn in their favor. For the market to fall is fast, to rise is can be a long wait. Brokers really need to fundamentally & technically updated in their endeavors & most importantly professional in their undertakings towards their client is investments mainly because there really not many profitable investments around to look at especially where the practices of governance r still superficially implemented by the relevant agencies.
Practice prudency & practical in ur approach.