In my experience, most of the fresh oranges & mandarins being sold taste mediocre to bad. There's no obvious way to tell without sampling them before purchase and grocery stores don't make this convenient. I think that if citrus brands were created that held a higher standard of quality they could pick up interest. Pink Lady brand cripp's pink apples are like this, only fruit that meets higher standards are branded.
From wikipedia:
"Pink Lady brand apples must meet certain trade mark quality specifications. Criteria for the specifications include sugar content, firmness, blemishes and colour. Inspections are regularly performed to ensure both the quality and traceability of the apple from the orchard to the shop."
These are pretty much the only apples I buy, even though they are more expensive. The only marketing I see for citrus is the Cuties brand which is pitching convenience but not exactly taste. They vary. Sunkist oranges are often bland. Inkagold mandarins too. I'm sure these brands have some standards but they need to raise the bar.
Maybe the problem is that only a small portion of the citrus crop is top quality compared to other fruit? Or varies more with the weather? I'm really not sure. I end up throwing away most of the sweet citrus I buy but the occasional great batch makes it worth trying.