They often send people away to get some other piece of paper, And they'll do it to the same individual many times, instead of tell them all the paperwork they need. Of course, they don't need any of that if the person pays an agent.
The extra tea money they generate goes to feed their families. I don't blame them but its a pain in the ass.
B) For price comparison, my condo does it for me for a fee of 100 baht
C) You can do it online
D) You can do it yourself, if your landlord provides you a contract, letter granting your permission to file the TM30, and signed photo of his ID/Passport.
At least that is the case in Pattaya.
EDIT: As seen in some of the other comments, doing it yourself may require photo copies of some other paperwork (chenute/deed, house book, I am not entirely sure what will be require).
"how can they deprive them of farang helping them out around the wat?"
The monks were getting by without farangs long before you were around and likely long after you are gone.
Technically "no". If you're going to spend a couple of days there then its no big deal. It becomes a big deal when you take jobs from Thais.
Once you've become accustom to the Thai ways, it will make sense or at least you'll learn to accept that it doesn't make sense (there some buddha for you).
I have been doing remote IT work in Thailand for the past 8 years. Mostly I have been on tourist visas. When I originally started this journey I looked into the Elite visa and found it was about the same value as other visa options. At that time, it cost half as much as it does now. My math worked like, $2500/year for 10 years... I needed for 8 years.. over pay by $5000, Or $1,200/trip, 2 trips a year... Effectively the choices, did I want to travel a couple times a year or did I want an elite visa.
I went with the tourist visas option. Today there are a few other visa options.
"I wonder if I would do the same" - Only you know you. But I suspect you already do... You own western goods? Cross Trainers? Microwaves? That comes to you by way of cheap labor. That's right some poor schmuck gets paid $10 dollars a day, lives in a dirt-floor hut, can't medicate his sick children so you could have a cheaper microwave. The difference between this scenario and the tourist scenario is only how close it is to you personally.
I often read Farang complain about the two-price system here. They complain that it's "unfair"... But considering income potential of the Farang, life is unfair. It's only the losers who complain about it.