Accounting for drivers that drive evening peak hours on Friday (weekday)

I want to ask a question about accounting for total rides that each rider drives in this case. 

TLDR: Why are drivers assumed to only be taking morning peak hour rides when there's an imbalance between evening rush hour hours between Mon-Thu and Fri?

We are given full details of the itinierary of the drivers in question and are told that they can only drive one of the rush-hours (peak hours) of either morning OR evening between Monday to Saturday. 

Note here that the peak evening hours from Monday - Thursday are 3 hours long while those for Friday and Saturday are 4 hours long (to account for an extra hour of night activities). Morning rush hours are only restricted to weekdays, as per the case text. 

The question then asks us to estimate the total hours that a rider drives: this makes sense as multiplying this value by the ride cost (constant) would give us the total revenue generated by 1 driver. 

However, the case solution states that it is “assuming our driver benefits from morning rush hour" such that the evening rush hour on the Friday is not accounted for, losing 1 hour of added revenue there. 

This justification makes no sense to me. There are evidently going to be drivers who choose to make 1 hours' worth of extra revenue to opt for Friday evening rush hours (3 hours on Mon-Thu vs 4 hours on Fri). I understand that between Mondays to Thursdays, the choice of morning or evening rush hour is irrelevant as the hours are the same and the revenue per ride is unchanged. 

Of course, this does (ultimately) have a huge effect on the answer of the total rides completed by a driver as this will vary based on the election of an evening Friday rush-hour slot or a morning Friday rush-hour slot. 

The commentary doesn't provide any justification for this and purely uses these assumptions to solve the case, failing to capture the alternative market of drivers who drive on Friday evenings.

Why does the case commentary make this assumption? Is there a justification for this that I've missed in this case or is my point valid and (potentially) highlights a flaw in the case? 

Going by the answer in exhibit 1, the case assumes that Friday evening is also a weekend (as it specifies 2 days worked in peak weekend AND we know that Sunday does not have peak hours), but this is not properly specified.