Why can charities keep asking for money without saying how much they need to solve the problem?

The poor you will always have with you.

The need is endless. Some charities do suggest amounts for the individual gifts but that is not always popular. 

Chuggers are a pest, but setting them a target would make them even worse.  

In many cases, the amount needed is unknown as they may be research charities. St. Jude's continues to do childhood cancer research AND they provide travel, housing and food etc to the patients and families. I checked them out at the site Malizz mentioned before I donated to them.

Any good organization will have goals, as to how much of an impact they expect to have with a certain amount of dollars but solving any problem takes more than money,  and even if it were just money, we probably wouldn't have enough. Know what I'm saying? Yo.

I would guess they have no idea.  What most disturbs me is that most don't tell me what and what percentage they spend on this or that, and what percentage they pay themselves. 

In England the larger charities pay there top managers Sums far in excess of one million proud a year.....All charities do it......
Greenpeace offices in Berckshire ,not so far from Winsor Castle have the most luxurious buildings and warehouses ever.....They have to spend the donations before the end of each tax year ,their storage facilities are strune  with so many expensive goodies.....

The Salvation Army headquarters in the city of London are the most Palatial officers you've ever seen.....They work in the most luxurious offices ever....all paid for by donations given to them ....

Needs are not so easily quantified.

not sure why, never heard of that

As others have pointed out, there are many causes with no particular end in sight. A lot of those causes do tell you what impact you're having. One ad that ran here this season told people "$X in donations buys seven meals." 

Giving that amount doesn't prevent fraud, though. 

Naturally, the more a charity is operated like a business, the greater impact it can have, and it's common for those who get into nonprofit jobs to earn 1/2 to 2/3 of what they did in the for-profit sector. They get into it because they love it and want to have an impact, not for a lavish salary. And, there are boards which dictate major decisions, so there are checks and balances in place. But, you do have to have things like marketers, coordinators, fundraisers, logistics experts, and so on employed if you're going to have a big reach. The question really comes in regarding how much of donations goes to the programming/ services offered versus overhead. There's a site called "Charity Watch" which identifies how much of spending goes to the program versus overhead and assigns a letter grade for the charity. For example, if 90-100% of funds raised go to programming, the charity gets an "A+." If it's 80-89%, the charity gets an "A." At 75-79%, the charity gets an "A-." At 72-74%, it gets a "B+" They consider anyone with an "A" to be highly-efficient. Anything in the C-range is is still acceptable/ average, which are places with 50% or more going to programming. 

Wounded Warrior is one that came under fire for excessive spending. They were "B-rated" at the time, with 74% going to programming costs. In the aftermath of the scandal, they lost 77 million in revenue.... That's just shy of $57 million veterans didn't get because people stopped donating. The biggest cut went to a trust fund for soldiers who had live-in caregivers who passed, and needed help to stay in their homes. No idea how many people that impacted. It's sad, really, considering they were spending more than most charities do on programming. Percentage-wise, they were doing a good job.

Was the spending excessive dollar-wise? Perhaps. They did a lot of giveaways and feel-good things for donors to get them excited about the programs and giving money. They were bringing in close to 400 million annually as a result. They were doing so much good for so many people, and now their reach is stunted. Fewer vets are getting help. 

As a donor, I understand there is overhead. I understand they have to spend money to make money. If 30 cents out of the dollar I give them goes to overhead, I'm cool with that. By spending that, they're amplifying their reach and generating more funds for a cause I believe in. That, in my opinion, is a worthy cause as well.

The March Of Dimes was originally dedicated to finding a cure for polio. Dr. Salk's discovery did that, so TMOD spent $65,000 looking for another cause, instead of declaring victory and getting actual jobs. They finally chose birth defects.