[1] The Logic is FREEDOM to use data at our will. One can use 20GB or more data on 90th day using 999 plan, but NOT in 499 plan.
[2] In 999, the chance of getting data wasted in almost nil. Suppose someone use less data during weekdays and use lots of data on weekends. For them daily 1GB plans have heavy wastage during weekdays and have to use COSTLY boosters (Rs301 = 10GB) during weekends. For them 999 plan makes sense.
[3] Further daily 1GB plans are the main reasons for daily data addiction. Almost everyone wants full paisa vasool and hence feels bad when most part of their 1GB data goes waste and so use youtube or others even though when there is no need.
[4] The speed (128kbps earlier) after daily FUP sux, which is further reduced to 64kbps by Jio now.
[5] Jio is badly in need of 999 plan users to beef up their ARPU. The ARPU of 999 with 90 days validity is Rs333 (it was Rs499.50 during 60 days validity times), whereas for Rs499, ARPU is less than Rs165. If there is NO takers for Rs999 type plans, then even Mota Bhai will become Chota Bhai, if you know what I mean...
I am NOT saying daily 1GB plans are pointless. It is suitable for almost 95% of the mobile data users. But still there is a niche for bulk data and / or data with NO daily limits. For example, after using around 500MB of data (for Google Play Music, Dropbox, Google Photos Sync, video song download using TubeMate), I got notification on my Samsung C9 PRO that an update of size 1408MB is waiting (Android 7.1.1). If I was using daily 1GB data, then I have to look for WiFi or recharge booster or plan during midnight (to use today's 500MB and tomorrow's 1GB). Since I am using 999 plan, I need NOT worry about anything and straight away started downloading.
Simply put, different people, different needs and hence different plans.