Why did the Rightly Guided Caliphs switch from tamattu ‘ to ifraad (in Hajj)?

The Rightly Guided Caliphs switched to enjoining ifraad in
Hajj for a reason they had when they thought that if people did tamattu‘ and
did Hajj and ‘Umrah in one journey, the Ka‘bah would be left with no one
visiting it in ‘Umrah and performing tawaaf and saa‘i (at other times of the
year), because travelling at that time was very hard and it was difficult
for a person to visit the Ka‘bah repeatedly. So if they were to do both
‘Umrah and Hajj in one trip and they limited themselves to that, for the
rest of the year the Ka‘bah would be neglected. So they thought that ifraad
was better so that the Ka‘bah would be visited throughout the year. They
interpreted the instructions of the Prophet (blessings and peace of Allah be
upon him), which was aimed at dispelling the false belief that prevailed
during the Jaahiliyyah, when the people of Jaahiliyyah used to say “ ‘Umrah
cannot be performed during the months of Hajj” and “When Safar comes to an
end and their posteriors have healed (from the effects of lengthy periods in
the saddle when travelling to for Hajj) and the tracks (of their mounts)
have vanished, it becomes permissible for the one who wants to do ‘Umrah to
do so”, meaning that no one could do ‘Umrah until sometime had passed after
Hajj. The purpose behind that was that the Ka‘bah should always be visited.
Hence Shaykh al-Islam (may Allah have mercy on him) said during his Hajj: If
a person does ‘Umrah only on one trip and Hajj only in one trip, in that
case ifraad is preferable, with no difference of opinion.” This is what he
said, may Allah have mercy on him. 

Perhaps he took that from the actions of the Rightly Guided Caliphs (may Allah be pleased with them), but one may feel uncomfortable with this view, so one could say that tamattu‘ is definitely best, because the Messenger (blessings and peace of Allah be upon him) enjoined it and encouraged it, and he did not say that it was only applicable for the one who had not visited before. As he did not make any exception, it is known that tamattu‘ is best and that the view of the Rightly Guided Caliphs (may Allah be pleased with them) was only on the basis of what they thought was best. But following the general meaning of the words of the Messenger (blessings and peace of Allah be upon him) is more appropriate. End quote.