Traditionally performers pay venues only for the right to use the space. If the performer wants the venue to sell tickets the venue charges an extra fee for this, and this fee is usually payable by the audience, this is the booking fee. Obviously they can use alternative ticketing providers such as ticketmaster instead, something that has become more common in recent decades, when major events have tended to rely much less on on the door ticket sales?
The performer (or promoter or agent) gets the entire ticket price - with the booking fee being the ticket sellers cut for the service of printing, selling and administering the tickets.
The reason the fee was not included was because different channels incurred different costs for the ticketing agent. Often on the door tickets incurred no fee as they cost next to nothing to administer and it was in venues interests to encourage full houses as it made the venue more attractive for performers.
Obviously these days it would be better Customer service to offer inclusive prices, with discounts where appropriate, but as such surcharges allow prices to be advertised that are lower than what the consumer ends up paying - a form of confusion marketing - there is no incentive to do this, other than if you wished to promote your business as being customer service oriented. As there is no effective competition (mostly if you want to see band X you have to use their agent) there is scant benefit to gaining a better reputation among ticket buyers.