"Juiced returns" is a consequence of some investment strategies, but not all. For example, if you aimed to hold a constant-maturity bond portfolio then that involves a degree of enforced trading - you need to sell shorter maturities and buy longer ones as time passes so that you don't end up with a year less maturity for each year the passes (or worse if defaults or other events lead to early calls or early payments without make-whole compensation). Likely you'd have got better than expected returns doing this (but then it was always a bet on falling rates).
But if you'd just bought a portfolio of bonds to give you a fixed bucket of maturities (which is what by far the larger part of the market has usually tended to do) and only reinvested cashflows as you received them from the issuers, you'd have likely underperformed your initial expectations because you faced reinvestment risk.
That lower return probably would have been compensated by inflation also falling for some of that time. But real yields have now been negative for quite a while, so to maintain returns you'd have been forced to accept more risk.
I’d guess that holding bonds until maturity in the form of a bond ladder was more common from 1980-2000, but since then bond funds have become more common.
I think large institutional investors buying credit (as opposed to treasuries - not sure what really happens there now) are still mostly following a buy and hold strategy. But yes, I'd agree that's likely the case for individuals (including through retirement accounts).
But if you'd just bought a portfolio of bonds to give you a fixed bucket of maturities (which is what by far the larger part of the market has usually tended to do) and only reinvested cashflows as you received them from the issuers, you'd have likely underperformed your initial expectations because you faced reinvestment risk.
That lower return probably would have been compensated by inflation also falling for some of that time. But real yields have now been negative for quite a while, so to maintain returns you'd have been forced to accept more risk.