I have a couple of things I can offer on the "doctors/lawyers" front, as my wife works with doctors all day, and I used to sell law firms all of their software and hardware for a couple of years. Some of it is not exclusive to the specific professions, but to the category of high wage earners.
For starters, they get a lot of expensive schooling with a lot of other people who frequently come from well to do families. The nice cars, homes and so forth are programmed into them. They tend to live beyond their means and measure their success based on their "stuff". Their family friends and those they met in college or in business are also high earner/high spenders. I've seen very few doctors/lawyers who didnt live in a huge house, own several expensive cars, eat in expensive restaurants all the time, etc.
I had a great example when I went to the dentist yesterday for a routine cleaning. I'm moderately well known in the dentists office as that "young guy that retired already". I've talked to the dentist who owns the practice and he confessed that he "bought high and sold low" for many years, figuring "how hard can this investing thing be, I'm a smart guy...?". A sentiment I've heard a lot in this crowd. After failing year after year and ultimately losing half his money in the 2000 crash, he turned his money over to a 2% money manager. Those who are learned in the "four pillars" know he's stepped from the frying pan into the fire.
Anyhow, he's got this "new" dentist on board. Just came out of retirement. I'm guessing he's in his late 60's, early 70's. Nice fella, seemed to know his stuff. He comes in to start poking me in the mouth with a sharp pointy thing and says "so you're the guy that retired early, I've heard of you!". After a few minutes of talking about his retirement, he starts talking about his airplane. Gets a picture of it and shows it to me. He spent two million on it. Says he used to have two planes, one seaplane and this one. Went on about his son the nerosurgeon who just laid out $300k for a ferrari and how he used to have one. Spoke with jubilation about his country club friend who just spent a half million on some special edition ferrari. I got the feeling that he was trying to 'measure up' with me after hearing I was an ER...assuming I'm loaded and he's going to impress me with his stuff. I didnt have the heart to tell him I drive a Ford, live in a modest home, have never owned an airplane or a ferrari, and frankly dont want any of that stuff!
I suppose that he's come back out of retirement to work for another dentist says that he must have lost some change in the 2000 downturn and needed a paycheck again.
The wife says the doctors at work talk about investing all the time, which hot stock they're buying, the beating they took on something they were talking about last month.
As far as going on their own and then hiring financial planners...well...many of the doctors and lawyers I know personally are incredibly, incredibly arrogant people. The mindset is that they're very smart and can do this investing thing on their own, and if they fail, the only way someone else could possibly succeed is if they're highly paid and as a correlation to that, even smarter than they are about this investing thing. I dont want to malign these professions...I think it takes a certain amount of self confidence to do them well.
So I guess the moral of the story is, it doesnt matter how smart you are, you arent going to win at stock picking as a part time speculation activity. Buying and selling on an emotional basis doesnt beat the market. Turning your money over to a financial planner for 1-2% a year wont help you either. Spending at or beyond your means will keep you working or even send you back to work. Growing up and maturing in an environment of big spenders handicaps you for living below your means.
As far as engineers and technical folk making up a big population of ER's here...well...thats easy...tech jobs paid pretty good in the last decade, tech people understand that other people are better at doing some things than they are, tech people are cheap, and tech people are more likely to use computers and yap amongst each other through online services.