I am writing this during the Ascension Triduum. You didn't know about that one?
It doesn't really exist, but given that part of the world celebrates the Ascension of Christ into heaven on Thursday, the 40th day of Easter, and part (including all of Latin Rite, Ordinary Form, Canada) celebrate on the following Sunday, one could be a little confused.
In places where The Ascension is celebrated on the 40th day of Easter, it is usually a Holy Day of Obligation. That means you must attend Mass, as you would on a Sunday.
Canada has only two Holy Days of Obligation, aside from Sundays. They are January 1, The Solemnity of Mary, Mother of God, and December 25, which is Christmas. It has been this way as long as I can remember.
I have never been told the reason that the Canadian Bishops decided to do away with most of our Holy Days of Obligation. The UK has four, the US could have as many as six, depending on the diocese and how the dates fall on the calendar.
I've heard a few arguments as to why it is a good idea to commute (move) celebrations of days such as the Ascension (or Pentecost) to the following Sunday. Some claim that families would have more difficulty gathering for Mass during the week.
I don't know if these are valid points. In present day, many families have difficulty gathering on ANY day of the week, for any reason. Should we also do away with the obligation to attend Mass on Sunday? Many have done so voluntarily, but that does not necessarily mean that all should follow suit.
I also note that Ash Wednesday and Good Friday, both of which are on weekdays and neither of which are days of obligation, are fairly well attended.
Although it was not so much the case when the decision to drop days of obligation was made, people work on Sundays almost as much as they do on weekdays. In Canada, more than in the United States or the United Kingdom, many bosses would likely have been at least nominally Catholic. They may have been more sympathetic to and even observant of holy days of obligation.
I have heard it said that by recognizing holy days of obligation during the week, we are condemning those who miss Mass to mortal sin. This would generally be true and also applied to Sundays. Something that must be remembered, is that the Church is a good mother. If we have serious reasons for missing Mass such as illness, legitimate employment, or caring for infants or others who cannot care for themselves and cannot attend Mass, we are not compelled to attend.
It would make sense for Masses on holy days to be offered in the evening or, where possible, during the day and the evening. This would allow for childcare options. Catholic schools could step up to the plate, so to speak, and hold Mass for the students.
Of one thing I am certain. By commuting holy days of obligation, we are missing out on a chance to visibly express our faith. "Sundays only" liturgical celebrations can get lost among the regular flow of Sunday Masses, or even denominational observances. I would even suggest that many people do not notice the feasts that are being celebrated on Sundays unless the homily specifically includes a reference to them.