I'm not sure what the fluff is for why Arcane Tricksters and Eldritch Knights don't have the ability to learn spells from scrolls, but they don't in the tabletop either despite being Intelligence casters and explicitly described to be practicing bits of wizardry by default.
I think its more they are melee fighters that know a few spells.. they focus on melee not spells so they have no time to specialise in mage work..
Yes, and to add to that, I interpret the difference between EK and AT and a full wizard as analogous to knowing how to say a few phrases in a foreign language versus being fully fluent. EKs and ATs learn a few specific spells and commit them to memory and can understand how to use a scroll that they find, but they don’t have the training, the experience, or the arcane literacy to compile a spell book full of incantations that they can prepare at will. They rely on rote memorization rather than the deep, granular comprehension of a true wizard.