Like if some clever game developer suddenly decided to map forward movement to the right trigger and shooting to analog stick up on a gamepad control scheme in a FPS.
It's one of these things which you won't be able to measure, but they will certainly have lost thousands* of people trying to switch to blender by this very simple default setting. This right here is a UX lesson - take note folks!
*probably, maybe
It's like with Emacs and its defaults. It wasn't breaking any convention originally, because there were no conventions back then, and it made sense for this particular case. Right-click selection was born before Blender, in Traces for Amiga. It was 1988 and the "standards" of today weren't established yet. Traces didn't become Blender directly, but this particular behavior has been carried over to it. Years have passed, and another convention won.
Maya, another software with quite a legacy, also has a lot of things considered archaic today. None of that is right-click selection tier, though.
The thing is, however, Blender is more than just a Maya/Max replacement. It can do a hell of a lot more. It has After Effects capabilities like compositing and video camera tracking, 2D animation tools, render outlines to SVG, video editing and python scripting. It’s a bit of a jack of all trades, master of some.
I won’t deny that it’s complex software but so are all professional 3D applications. Try and use Solidworks or (shudder) Creo/ProE or Maya or Max and selecting a cube will be the least of your issues.
All of these tools require some degree of training that’s part of the landscape.
Personal anecdote:
The first 3D software I used was Cinema 4D. I couldn't be bothered to watch a tutorial, but in a good 10 minutes of clicking around, I could already do more than half of the most common operations. I tried using Blender several times before and after that, but after the same amount of time, I couldn't do literally anything. Not even move the cube! After switching to Linux, I finally forced myself to watch a few Blender tutorials. I can now do things better and more efficiently than I ever could in C4D. But the moment I switch to another tool (Unreal/Krita/Inkscape...), I see just how non-standard Blender is. There's always the Blender way and the everything-else way.
2.8 is a huge step in the right direction. Maybe one day multi-select will make sense and then there will be no more reasons not to use Blender.
So I wouldn't say that Blender's controls are inherently obtuse or more difficult than others, but that other popular software follows conventions that are more familiar to people with a subset of similar experiences.
The controls in Blender are so terrible for me I've basically always given up in frustration within an hour or so.
The reason I didn't customize the controls is because I shuddered at how awful the UI for doing that probably was, and feared other lurking UI terrors were I to invest in adopting the app.
I find it very off putting that suddenly all existing tutorials and manuals might become bogus.
Pretty much the only tool where I have custom bindings is Vim.
It is better than most commercial offerings on OSx, and yet, everyone still threats it as a poor hack by mangling the UI by default.
Give blender a "copy after fx UI" default already.
That said I'm completely blown away by the quality of blender. It is among the most well polished applications I've ever had the fortune of using. And an open source software at that, and multi-platform at that.
Truly amazing.
ZBrush UI is also alien and counterintuitive, but after you learn it it begins making sense and feeling convenient, not so in blender, here I have to fight it for no reason.
But god damn I’ve never even gotten close to being comfortable using their interface. Every tutorial online seems to be flawed in some way, so that you have to look up another tutorial to find some feature. I really can’t follow the logic they use to organize things. Is there a feature where you can type the name of a function into a search and it just pops up? If so I’d probably save 80+% of my time spent in the program.
This change also has received some backlash from the existing userbase, albeit you can configure the behavior.
New users don't know how to fix the behaviour. They just leave.
Because they wanted to develop Blender for Blender users.
This is probably the biggest feature in 2.8! The super non-standard select behavior was a (probably unfairly, but still real) turn off to people trying Blender for the first time. The more Blender can bring its UI in line with industry standards the better for Blender adoption.