It is common practice for the chip-level DTSI to define the range of (known, usable) capabilities of the chip and then have the DTS enable what is actually usable for that board. Especially for things like I2C, the connections to the SoC pins may not be available.
make menuconfig selects things, but doesn't change them. The DTS and what it includes are defined on a board-by-board basis, and set the limits of what might be meaningful to add to the firmware. As there are around a thousand boards supported, it would be a maintenance nightmare to have the config process reflect all the hardware variants in dependencies, not to mention making the dependency display completely unreadable.
Assuming that you can get I2C slaves recognized and the I2C connection is "easy", submitting a patch setting the I2C node to "okay" for your specific board would be the next step.