Online tickets less than 90 minutes before departure
 

Is there any sensible reason why tickets cannot be purchased online less than 90 minutes before departure? It appears to be a means to impose a (possibly very significant) financial penalty on those who need to travel at short notice on the last train of the day?

If I need to travel with less than 90 minutes notice on a train other than the final train of the day, I can simply purchase a flexible ticket for a later train and use it (minus seat reservation) on the train it's too late to buy a ticket for.

But if I need to travel at such short notice on the last train of the day, I can't do this - the first train I can book is tomorrow so the ticket wouldn't be valid today. I must pay the full walk-up fare, which could be more than double the price of the most expensive flexible online ticket.

I can purchase a ticket online for the very same train from a station further up the line, as long as the train leaves that station in more than 90 minutes. But it's a breach of the conditions of carriage to use more than one ticket on a single train if it saves you money, so doing this and just paying the walk-up fare to that point isn't allowed.

I seem to even be able to purchase a ticket from a station that same train is due to leave in more than 90 minutes, while the train is already moving which makes a mockery of the excuse I'm sure I've read somewhere that closing bookings a certain time before departure from origin is to ensure seat reservations are displayed.

Reservations booked along the route after 90 minute cut off for terminus departures rarely display. Additionally boarding for a service can start anywhere from 60 minutes before departure. It would not be fair for a customer to sit in a free seat only for someone to book lets say 30 minutes before departure.

90 mins is short compared to many other operators.

It makes sense to disallow seat reservations 90 mins before departure. However it would still make sense to allow tickets to be purchased with no seat reservation. Especially if travelling from a station with no TVM.