Why are the feasts of the Epiphany, the Ascension and Corpus Christi transferred to the following Sunday in other countries?

The Holy Days of Obligation in the Roman Catholic Church are observed:

“On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass. Moreover, they are to abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body.”- Code of Canon Law, 1247

The Code of Canon Law stipulated the list of the holy days of obligation:

“Sunday, on which by apostolic tradition the paschal mystery is celebrated, must be observed in the universal Church as the primordial holy day of obligation. The following days must also be observed: the Nativity of our Lord Jesus Christ, the Epiphany, the Ascension, the Body and Blood of Christ, Holy Mary the Mother of God, her Immaculate Conception, her Assumption, Saint Joseph, Saint Peter and Saint Paul the Apostles, and All Saints.”

- Code of Canon Law, 1246 §1.

THEREFORE,

1 January: Solemnity of Mary, Mother of God

6 January: the Epiphany

19 March: Solemnity of St. Joseph, Husband of the Blessed Virgin Mary

Thursday of the sixth week of Easter: the Ascension  (40 days after Easter)

Thursday after Trinity Sunday: the Body and Blood of Christ

29 June: Solemnity of Saints Peter and Paul, Apostles

15 August: the Assumption of the Blessed Virgin Mary

1 November: All Saints

8 December: the Feast of the Immaculate Conception of the Blessed Virgin Mary

25 December: the Nativity of our Lord Jesus Christ (Christmas)

FURTHERMORE, “with the prior approval of the Apostolic See, however, the conference of bishops can suppress some of the holy days of obligation or transfer them to a Sunday.” (Canon  1246 §2.)

There some countries who even added holy days of obligation in the aforementioned list. Ireland, for example, has Saint Patrick's Day; Germany has St. Stephen on the "Second Christmas Day" (26 December), Easter Monday and Pentecost Monday (Whit Monday).

In the Philippines, we observe the following solemnities and feasts as holy days of obligation:

1 January: Solemnity of Mary, Mother of God

8 December: the Feast of the Immaculate Conception of the Blessed Virgin Mary

25 December: the Nativity of our Lord Jesus Christ (Christmas)

Note: All the other Holy days of Obligation are either dispensed or transferred to the succeeding Sunday.

Through the prerogative of the Catholic Bishops’ Conference of the Philippines (CPCP) with the approval of the Holy See (cf. canon  1246 §2), the following feasts are transferred to the following Sunday as their proper day for pastoral reasons:

1. The Epiphany to the Sunday that falls between 2 and 8 January

2. The Ascension of Our Lord to the following Sunday;

3. The Body and Blood of Christ to the following Sunday.

Since these three feasts are assigned to a Sunday, they are NOT included in the list of holy days of obligation, since in every country all Sundays are holy days of obligation. The General Norms for the Liturgical Year and the Calendar (no. 7) states that:

“In those places where the solemnities of Epiphany, Ascension, and Corpus Christi are not observed as holydays of obligation, they are assigned to a Sunday, which is then considered their proper day in calendar. Thus:

a. Epiphany, to the Sunday falling between 2 January and 8 January;

b. Ascension, to the Seventh Sunday of Easter;

c. the solemnity of Corpus Christi, to the Sunday after Trinity Sunday.”

The Vatican City (but not in the rest of the Diocese of Rome) and the Swiss canton of Ticino are the ONLY places where Sundays and all ten days listed in canon 1246 are observed as holy days of obligation.