If meniere's is now affecting my second ear, why shouldn't the doctors section the vestibular nerve in this ear as they did with the first one?

Not necessarily: Vestibular nerve section is reserved for meniere's patients who have severe attacks of vertigo that persist despite maximal medical therapy and who still have good hearing levels in the affected ear. Usually the patient has also tried and failed intratympanic steroid injections to try to improve the episodes of vertigo.

Both ears Meniere's: Sectioning both vestibular nerves will remove the inners ears from balance detection, and may create an untreatable sense of instability or rocking called oscillopsia. All other treatment shouls be tried.