They weren't the same Elves Tyrande was speaking to. Because the Elves she was speaking to not only were in open rebellion against Elisande, they already tried an insurrection once, before the lowering of the gates, in order to prevent that. Which almost cost the very Elf Tyrande was talking to specifically her life. So it's kinda hard not to trust someone not to repeat the same mistake again when they haven't made it the first time yet. You're godawful at context.