Last time I flew to the US, I wasn't given a CBP form (this is where one would normally declare stuff). If the airports have gone paperless (I'm not sure if all airports have done so and how to check if a particular airport has; probably this is a topic for another question), how do I declare some food when entering the US? (If it matters, by food I mean chocolate, canned food, dried fish.)
For those paperless airports, instead of filling out the paper form, you go to a kiosk where you fill out all the same information. Some of it is pre-populated from you swiping your passport at the kiosk, but then it will ask you the same questions the paper form does. It then prints a copy of the form that you hand to the customs officer.
See this website for more details, including the following blurb:
No, travelers will submit their Customs declaration form electronically via the kiosks. If a traveler has already filled out a Customs declaration form, it can be given to a CBP Officer for shredding.
Over the past few years most US airports have increase the use of electronic submission of the "blue" customs form - either via APC Kiosks which can be used by US citizens and Permanent Residents, Canadian Citizens, people travelling under ESTA, and specific visa holders including the most popular B1/B2 visas, or via the Mobile Passport Control app that can be used by US and Canadian citizens only at this stage.
However there are still a (relatively) small number of people that are required to use the standard immigration lines, and these passengers still need to fill out the blue form.
Airlines have changes the procedures for handing out forms on-board - where previously they would blindly give one to every passenger (or at least, one per family) some now make a point of announcing that only some visa holders require them, and only offering them as required. From what you've said it's possible some airlines are only giving them out to people that ask them for, or even not at all (although I haven't personally experienced that).
If you do not receive a form on-board, they are also available in the immigration hall before you reach the immigration staff - generally at the back near where you enter, and normally with a desk area available to fill them in, although this will vary depending on the airport.