Praise be to Allah.
Undoubtedly offering food is one of the noblest of characteristics and a sign of generosity, and it is encouraged in Islam. It was narrated that ‘Abd-Allaah ibn Salaam (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “O people, spread salaam, give food, and pray when the people are sleeping; you will enter Paradise in peace and safety.” Narrated by al-Tirmidhi (2485)’ classed as saheeh by al-Albaani in Saheeh al-Tirmidhi.
Islam enjoins honouring one's guest and giving him his due. It was narrated that Abu Hurayrah said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever believes in Allah and the Last Day, let him honour his guest.” Narrated by al-Bukhaari (6018) and Muslim (47).
What is meant by the guest whom it is obligatory to honour is the guest who is travelling, who is coming from another city or country, not the visitor who is a neighbour or friend from the same city. Honouring this latter (the visitor) is required and comes under the general teachings of Islam which encourage doing good, treating people kindly and having a good attitude towards them. So it is the guest who is a traveller who is the one who has the right of food offered to the guest. This does not apply to the visitor whom one may tell to go back, as Allaah says (interpretation of the meaning): “And if you are asked to go back, go back, for it is purer for you. And Allaah is All‑Knower of what you do” [al-Noor 24:28].
See also the answer to question number 128791.
Based on that, there is nothing wrong with what the people referred to in the question are doing.
Moreover, even if we assume that they are guests of the type whom it is obligatory to honour, if they themselves agree to waive their rights and say that they will bring food with them, there is nothing wrong with that.
Hence we do not think that this action is contrary to sharee’ah or generosity; rather it is indicative of the close and strong ties that they have with one another.
We appreciate your eagerness for the Sunnah and we ask Allah to grant us and you deep understanding of His religion and to make us steadfast in following the truth.
And Allah knows best.