One of the reasons why the FooEvents Bookings plugin is not included in the FooEvents Premium bundle is to keep the cost of the FooEvents Premium bundle as low as possible. The booking slot functionality in the FooEvents Bookings plugin is an extra feature with added value, since the core FooEvents for WooCommerce plugin and FooEvents Multi-day plugin extension have always only focused on events where all attendees attend on the same date(s) e.g. a concert, multi-day conference etc.
Another reason why they are not currently part of the same bundle is because the FooEvents Bookings and FooEvents Multi-day plugins are not specifically integrated with each other since they are intended to be used in different ways. The FooEvents Multi-day plugin is better suited to events that span over multiple days and where all attendees are expected to attend all the days. It does not let your customers choose a date, but can work well if you are selling passes since it allows check-ins on more than one day/session. The FooEvents Bookings plugin lets your customers choose a specific date and/or time slot.