That's a very good point - the world of work is changing, fewer and fewer people work 9-5 and the railways should reflect this - a lot of people work flexibly and/or from home 1 or 2 days a week, a "loadable" season ticket which is on an Oyster▸ card type system and is valid for 30 days worth of trips rather than a calendar month would be a good step forward.
Exasperatingly
GWR▸ have known about a low-tech solution to this for a few years but haven't rolled it out.
In Cornwall and Devon, on selected routes, you can buy part-time season tickets: valid for three selected weekdays, plus weekends. The route section of the ticket says "MO TU WE &WKND" or whatever combination you buy it for.
Here's a typical BRFares link.
But it's only available there, not across the whole GWR network. So part-timers (at least the ones I know) watch like a hawk for advances to become available on their working days, and then spend the evening in front of a computer booking as many as possible. This isn't a sensible solution for anyone.
That's a good step but it's still only half a solution, because of the need to select your weekdays. It does nothing for the truly flexible worker or those on rolling shifts, who might be working Monday, Tuesday, Wednesday this week but Tuesday, Thursday, Friday next week (or indeed just Wednesday this week but five days next week, etc). As TG says, a "carnet like" system allowing n journeys over a period of m days would better address the needs of "modern commuting". Nevertheless, it's good to see even this. Shame it's so geographically restricted.