I don’t know the full history, but I presume the upfronts were an artifact of the early days, when a sponsor took an entire program, not just spots in it. So it was the “Camel Caravan with John Cameron Swayze” or “Kraft Music Hall” etc. The only commercials in the show were for the one sponsor - and there was less time devoted to them. (In fact for many the program was produced by the ad agency.)
Flash forward a decade, and sponsoring a single show blew the advertiser’s wad in a single half hour, so they started breaking up the spending, buying “minutes” in multiple shows. At this point the networks, which had retaken production control, started the upfronts, to introduce bigwig advertisers to new shows, and sign contracts for intents for the following season. Done in venues as large as Radio City (but often smaller) it was a schmoozefest, autograph session, big star spectacle - and the actual business was done over the next couple weeks as advertisers signed “almost secure” contracts for various shows and/or time blocks. [Almost secure: if a show drastically underperformed in the ratings the network would “make good” (free) spots in other venues.]
Anyway, the amount of advertising went up - from 8 minutes/hr at the very beginning to 12 then to 16 within a decade, where it more or less hovered for the next decades. (Not including the intrusion of the “bug” promos in the lower right corner of the screen)
With a single sponsor, how many times could you see the same commercial/sponsor in a single program? As that model broke up the “variety” of spots allowed for more commercial time, as well. For a while the NAB set the max at 14 (I think), then 16 minutes/hr.
I am unaware of any similar gargantuan events in radio, at least once network radio of the 40’s & 50’s collapsed in favor of DJ’s & music, although I’m sure there were meet and greets for the few truly national programs like Limbaugh, Larry King, Casey Kasem, etc. Never participated in anything like that, so I don’t really know.
But for your question about radio: yes, ad time increased with consolidation, partially because of the weakening of regulation and decimation of the FCC in the 80’s, partly because of financial pressures to perform. And one other factor: the micronization of message: in the beginning spots were :60 seconds. Then :30, although advertisers would pay 75%-80% as much as for a :60, they could reach many more listeners more often. Then came the :15 or the :20 or even :10 (Metro Traffic, for instance.)
I have seen research demonstrating that people hear “interruption” more than “length.” That is, 2-:30 spots sound longer to listeners than 1-:60. Now take a cluster, as TV is programmed (and some badly formatted radio), and pack it with 8 to 10 :30 second commercials and it seems interminable. Meanwhile the advertiser reaches a wider audience, the network makes more, and the thing thats lost is “less attention paid” to the 4th commercial in the chain.
Ah, back to the negotiation process for the upfronts: no, nothing like Dutch auction. Good old fashioned Mad Men, liquid lunches, good-ole-boy hondling and handling, Very used car salesman approach, and “sign here, press down there are carbons.” The process could go on for days, weeks.
And of course about 30% of inventory was reserved for the “scatter” market, opportunistic times that an advertiser hadn’t foreseen, or a sudden hit show a network can milk, or, as mentioned above, make goods for under-delivery. Sometimes the scatter inventory was just “inventory that didn’t sell upfront”. Sometimes it was purposefully reserved.
Research was rudimentary by today’s standards, but yes demographics, and even in some cases product consumption stats to help push the price higher.
Product placement? Hardly new. One of the early shows, “Leave it To Beaver” (or similar, not sure) was produced by Westinghouse’s and agency, which is why there were so many family discussions in the kitchen, all the better to see the Westinghouse appliances in the background throughout the show. Everything old is new again.