The only way this would actually be a logical argument is if the owners were allowing seats to go unsold rather than sell them at a reasonable price.
In the vast majority of instances this isn't the case. Demand outstrips supply. There are enough people who want to and can afford to pay hundreds of pounds to see Taylor Swift/Coldplay/Oasis or Rachel Zegler or Leslie Odom Jr, or Man United, to sell out the venue.
Therefore why does it matter whether the criteria for getting a seat is money based rather than any other form of exclusion? Either way, not everyone will get what they want.
Or, to make it as simple as possible, a theatre can only seat 500 people. If 1000 people want to see that show, then even if you allocated the tickets for free via a random lottery, 500 people are going to be disappointed.
Actually, even if you gave the tickets away, there would still be people who couldn't come, whether it's because of ill health, because they live too far away, because they can't get time off work, can't get a babysitter, or would still need to pay for hotels and travel and can't afford that. You could equally say it's not fair that people living closer to London have more opportunity to see shows, or people who have flexible working patterns, or people in good health.
Life isn't fair. Not getting something you want because you can't afford it isn't more unfair than any other means of restriction.
Why should "the ordinary working person" be entitled to watch a premier league football match or have a good seat at a megastar concert, but people don't apply the same argument to owning a designer handbag or a Porsche? They are all luxury purchases that you can live without. Why is it acceptable to whine if you can't afford some things, but not others?