Well.... "serious" anyway. It's more marketing than anything. If regular drone delivery ever becomes commonplace it's won't be anytime soon.

It's just not realistic from a legal or economic perspective. The FAA has only recently begun issuing exemptions and COA's for civil operators. The upcoming regulations are not looking conducive for delivery services either. They include weight limits of 55lb (including payload), a licensed pilot, a visual observer, operational limits like hight restrictions and most importantly maintaining line-of-sight.

That's before you consider whether it makes economic sense too. Hint: it doesn't, even if you don't have to pay the pilot and observer in the future due to relaxed rule as fully autonomous drones become safer and more reliable.

First, you're legaly and realisticly limited in weight.

Which means the range of items it even makes sense to deliver is reduced to lightweight high profit items. You're not going to waist time buying a $10k+ delivery system to deliver items you only make a buck on after all.

Second is all the ancillary costs.

Energy use and costs will be higher, flight isn't exactly efficient transportation we have, even less so with multicopter flight.

Then you have risk factors like loosing drones and payloads with associated insurance cost, or even worse hitting someone or something. Now you're ristrected to "shipping lanes". If insurance or the FAA doesn't make you NIMBY's will over noise and general risk concerns.

I'll stop here, but you see it's already at the point of why even consider something like this over anything at least slightly more realistic like autonomous delivery bikes?

TL:DR; The answer is drones have been in the public eye and are "cool." It's marketing and everyone fell for it.