There is never a good reason for using language this obtuse, but there's lots of bad reasons.
This measure in particular seems engineered to be just clear enough to be upheld by a judge, but also sufficiently obfuscated so that the public doesn't know what it's actually voting on.
Sure but if you literally cannot understand it, it may be difficult to determine whether voting against it means voting yes or no.
The main reason for the verbal atrocity is legislators had to cram a more or less complete description into a single sentence, per constitutional requirements.
Or the other common reason, that they campaigned on getting a measure to the ballot that has voter support, but they don't want it to pass. The first thing you do is come up with a confusing text with extra points for double negatives, and you follow that up with a confusing media campaign.
You may fail, and it passes with 87%, but sometimes if you work hard enough you can get Illinois to vote down a progressive income tax.