One of the properties of LEDs is that in one respect they act like Zener diodes. In an environment with limited current, they don't pass any current until the voltage presented to them goes above their forward voltage. A Zener just passes current at that point, and regulates the voltage across itself atwhatever voltage it says on its label. Very handy when making a voltage regulator. An LED also regulates its voltage, but lights up as well.
Putting two or more in parallel, the one with the lowest forward voltage wins and lights up. The rest never see their "lighting-up voltage", and don't.
Having one, single, resistor of too high a value will, even if all the LEDs get to their illuminating voltage (assuming they all want the same) they will light up, but
not as brightly, because the current through the resistor will be distributed among the LEDs, so each one gets less.
If the LEDs have a wide enough spread, thenthe lowest voltage one will win for a time, then it will die, and the process will repeat until there are no LEDs left in circuit.
If anybody wants to understand basic electronic components, then
https://archive.org/details/PracticalElectronicsHandbook/mode/2up has a free download option. Although a technical book, it is in real English, rather than college technical.