Domesticating trees is hard and takes a really long time combined with the fact that oaks just aren’t a very good food source.
It’s rather telling that, despite the fact that there are hundreds of oak species, probably dozens of palatable oaks, with ranges including almost every major human civilization (Europe, the near East, China, Mezoamerica), none of them were domesticated. We domesticated filberts, walnuts, chestnuts, various pine nuts, podocarps, pecans, pistachios, torreya, macadamias, cashews, candlenut, hazelnuts, almonds, heartnuts, and who knows what else. Yet nobody ever domesticated an oak. Or beech for that matter. I doubt it was for lack of trying.
Oaks probably just aren’t actually very fit for human consumption. That’s the thing with a lot of non-traditional crops–they often aren’t traditional for a reason.
If I had to take a stab at specific reasons, oaks are usually highly alternate-bearing, have a very long juvenile stage, are wind-pollinated, and outcross and hybridize easily (bad if you are trying to stabilize traits). The nut is small, does not have a protective shell but has an adherent skin, so they suffer from animal predation while still being hard to process efficiently, and is very high in tannins. Acorns are high in unsaturated fats, which, combined with the thin skin and lack of shell, means that they go rancid quickly, and if you did breed out the tannins, they’d go rancid even faster (tannins are anti-oxidants, so they slow down the process of going rancid–tannins are also pretty toxic to the liver, so please don’t start trying to eat a bunch of acorns on the assumption that they’ll prevent cancer because of the high levels of antioxidants…).
Some crops are well-suited to domestication, some aren’t. And some crops are well-suited to feeding large numbers of people; generally speaking, crops that have a lot of calories that also store well. Which is to say, carbs. Most seeds high in oils go rancid in storage, seeds high in protein are uncommon and typically don’t have as many calories since protein is biologically “expensive” to make. That leaves carbs. Corn, wheat, barley, rice, cassava, potatoes, sweet potatoes, yams, breadfruit, the list goes on. All rich in carbs. All human staples. That wasn’t by accident.
Arguably, in the modern day and age, the parameters of what makes a good staple crop have changed. Processing and storage is vastly better now, so we can rely more on oily seeds. And now that I think about it, we actually have done some recent domestications as a result. Canola simply wasn’t edible until recently, and palm oil was of pretty iffy quality, but we’ve used breeding and better processing to make canola and palm oils into a keystone of the modern diet. For better or worse.