Ok, I'm new to learning about this stuff (spent 18 of the last 24 hours reading about AOR, MS, etc).

Already assuming I am able to clear out bonuses within the original time frame. Some CC's (mainly chase ink) provide very strong cash back programs. This sentence below made me think:
Earn 5X points per $1 on the first $50,000 spent in combined purchases at office supply stores and on cellular phone, landline, internet and cable TV services each account anniversary year.

Currently the bonus offer is 50K for $5K spend. Assume I spend 5K in month 1. That equates to $500 worth of points. Then from months 2-12 I spend 4K a month on MS through GC's at various office supply stores. $4,000 x 5% cashback = $200/month in cashback just for loading up. In that year someone can get $2,700 in cashback rewards after $49K is spent (average 5.5% cash back). Excluding some random fees occurring and annual fees..

As mentioned before, my initial thoughts were that people used MS to clear sign-up rewards and I haven't seen much of people continuing using it to get additional reward money back. Is there something I'm missing here? Or do most people keep getting new cards because the sign-up reward is more lucrative than just grinding high cash-back offers? Or is it because after awhile it will become quite obvious after awhile that MS is happening based on consistent buying patterns?