They can’t, they’d have to pay the old guy.
He refused to return in Wrath due to ‘‘embarrassingly low amount’’ of money offered for it, so… That’s why they changed him. I kinda like the newer Arthas (Patrick Seitz) over the old one… more anger.
She does have a new voice actress, yes. OG one from WC3 don’t voice her anymore. She sounds a bit too girly (as in, she sounds like a small girl over an adult) imo…
Jaina’s always had the same VA as far as I know.
Sylvanas’s new voice threw me off a bit to begin with but I am really impressed by Patty Mattson’s performance
Old one was more mysterious. This VA does not do Syl justice imo.
Carrie Gordon Lowrey was her Pre-Wrath voice actress, now it’s Laura Bailey since Wrath.
Carrie voiced the nightborne child in Suramar though, Korine!
I checked and confirmed this - my mistake. Laura is an exceptional VA and singer so I am very happy with the casting there (and most of the VA casting in general)
Peeve: I missed out on the Vulpera argument.
You’re losing your touch, man.
I’m loosing my religion.
You’re a deity yourself.
No, Deity is someone else
argh why must I always be clowned on
You’re a master clowner yourself though! 
The real crime is what they did with Kerrigan’s voice actress…
I like her StarCraft 2 voice…
I like it too. Tricia Helfer’s a fine actress.
But Kerrigan’s original voice actress, Glynnis Campbell, was better. Moreover, Blizzard ditched her for no reason. Not even a token “pay dispute” - they just didn’t take her back when she offered to come back, because… well, Helfer was “more recognizable to new players”, apparently?
shrug
Why did they change Sylvanas WC3 voice actress? I mean, the OG one was far superior than the ones after WC3, but they changed her for no reason there too…
'Tis a shame. I even prefered the OG voices for the Nathrezim, but they were changed too. 
From various interviews, Blizzard has apparantly been very difficult towards their OG voice actors. Several of the old Wc3 ones when you google, the most prominent being wc3 Arthas, has spoken out that they have either just flat out declined them work again, or for laughably low payment. The general attitude seem to be that unless it’s a “famous” VA, they don’t really care much and will either offer them next to nothing and/or treat them extremly poorly.
Only VA that I’ve heard off that they didn’t keep for an actual reason was Terenas because he died around the time wc3 was released.
They kept the OG Archimonde, David Lodge. Though he did a better voice in WC3 than in WoW. The OG Mannoroth returned for Cataclysm, but he wasn’t the VA for WoD.
'Tis a shame.