Here's a simulation to answer your question:
Would we not expect to have a seen a greater decay than what has occurred so far?
The simulation includes the Newtonian and the relativistic accelerations of all the planets, Sun and Moon.
The Earth's gravity field is modeled with the SGG-UGM-1 gravity model (computed using EGM2008 derived gravity ...
This additional answer is just to show the effect of the solar activity on the decay rate.
The graphs were obtained from 15279 TLEs downloaded from https://celestrak.com/NORAD/archives/request.php processed with the CSpOC's SGP4 library freely downloadable from www.space-track.org.
The following graph shows the mean radius vector and the mean air density (...
In this supplementary answer I've crudely processed all TLEs for Vanguard 1 and plotted the trends.
I used the mean motion (revs/day) to get a period, divided by 0.9975 (estimating from this answer) to undo the effects of $J_2$, then used $a^3=GM (T/2 \pi)^2$ to estimate a semimajor axis, periapsis and apoapsis based on the TLE's eccentricity value. This is ...
Because it's using Earth's magnetic field to create drag. It's one of several passive deorbiting systems.
An electromagnetic tether uses a conductive tether to generate an electromagnetic force as the tether system moves relative to Earth’s magnetic field.
NASA: State of the Art of Small Spacecraft Technology, 12. Passive Deorbit Systems
Removing debris costs money.
Even with many words like "efficient", "low-cost", and so forth, a system capable of removing a significant amount of space debris still involves a budget requirement containing a large number of digits.
For other space programs, the motivation for the large sums of money spent is a gain of some sort. Scientific data, military ...