It's not just the last 8 years. WotC have produced maybe half a dozen good adventures, ever.
And, in fact, TSR put out painfully few good modules in the whole of 2nd Edition, and indeed much of the 1st Ed output was of questionable content. And, indeed, virtually every game, ever, has either had little adventure support, or those adventures have been generally poor.
To a certain extent, it's because "adventures don't sell", and that's a self-fulfilling prophecy. Because adventures don't sell, they're done as an after-thought, not given the resources they need, or worked on by inexperienced people. Thus, the quality suffers. Because the quality is poor, word gets around and people refuse to buy. And because they don't sell, the next batch get even less attention...
It is quite notable that the companies who make adventures the centre of their business (primarily Paizo now, but in the past that included Necromancer, Goodman and even Green Ronin) became noted for their adventures, saw decent sales, and were thus able to thrive. Good adventures sell, but you have to build (and keep) a reputation for good adventures, or you're sunk before you start.
So, I would dearly love to see good adventures for 5e (whether from WotC or the third-party publishers). But I wouldn't hold my breath.