I can't see what 会 is doing in this sentence. Maybe nothing, could it just be omitted??
当初为什么会转行呢
Which I would translate as: 'Back then, why did you change your profession?'
会 here simply means "would"
"当初为什转行呢?" = "Why did you change job back then?"
"当初为什么会转行呢?" = "Why would you change job back then?"
more example:
"你為何同意?" = "Why do you agree?"
"你為何會同意?" = "Why would you agree?"
Yes, you can omit it, However "would" in the sentence does emphasize an inquisitive tone. Imply "you should not had."
“会”,it can mean "meeting". For example, "我在开会” I'm having a meeting. it can also mean "a modal particles". for example, "你怎么会转行呢?" why did you change your profession? "你怎么转行呢?"why did you change you profession? the later sentences be lack of euphemism tone!
It can be omitted. Check this: Why did you change your profession? Why did you choose to change your profession? Not much difference, right? This doesnt mean that 会 is equal to 'choose to'.