[Grammar] Or perhaps it’s that

Make the decision.
This step, surprisingly, is sometimes overlooked. Perhaps that’s because the intellectual wrestling required in the previous steps can seem exhaustive, leaving little energy for the final decision. Or perhaps it’s that a quasi-academic mind-set comes into play, confusing analysis with action and failing to move from the theoretical to the practical.
(How Good People Make Tough Choices; R. M. Kidder)

Would you be so kind as to tell me what is the grammatical role of 'that' here?

Thanks.

Here, that means because.

Thank you Charlie Bernstein!

Charlie Bernstein said:

Here, that means because.

Click to expand...

I've figured it out, but to my dismay I couldn't find in any of my dictionaries 'because' as one of the meanings of 'that' -- would you be so kind as to point me to such a dictionary article if you happen to have come across one?

Thanks.

No, sorry. But this might help:

Pronouns always refer to a specific noun. But - sometimes the noun is not stated. In your paragraph, you have two pronouns that both refer to the same unstated noun:

This step, surprisingly, is sometimes overlooked. Perhaps that’s [meaning: the reason is] because the intellectual wrestling required in the previous steps can seem exhaustive, leaving little energy for the final decision. Or perhaps it’s [the reason is] that a quasi-academic mind-set comes into play, confusing analysis with action and failing to move from the theoretical to the practical.

So the red-highlighted "that" and "it" refer to the reason why the step is overlooked. Now the sentence is clearer, right?