Rashi citing Targum Yonasan: Malchus Beis David, which leads them gently, like a Shilu'ach that flows gently. Shilu'ach is a spring; it is called also Gichon. They wanted to remove Malchus Beis David in the days of Achaz to Pekach ben Remalyahu. Here is a Nevu'ah about Shevna and his cohorts, who wanted to rebel against Chizkiyah. They despised him, for he did not choose the king's table (to eat royally), rather, to eat a measure of vegetables and engage in Torah. It says about him "Tzadik Ochel l'Sova Nafsho" (Mishlei 13:25). They had seen Pekach ben Remalyahu eat 40 Sa'im ¹ of chicks for desert (Sanhedrin 94b), and derided Chizkiyah - is he proper to be king?! Rather, Retzin and Ben Remalyahu were proper to be king in their lifetimes.

Radak: In the days of Achaz, in Yehudah and Yerushalayim, many despised Malchus Beis David, because it was weak, and wanted the strong Malchus Efrayim. It mentions Retzin together with Pekach, for they fought together against Yehudah. Malchus Beis David is compared to a small river that goes slowly, for it lacked power to harm their enemies Retzin and Pekach.

Malbim: The custom was to anoint kings by springs. Malchei Ben David were anointed by Mei ha'Shilu'ach, a small spring that flows gently, for a sign that their kingship will last gently and securely. The people despised this calm kingship.

Rashi: Shevna and his cohorts despised Chizkiyah for his meager eating. They said that Retzin was proper to be king. Hashem said, if you desire eaters, I will bring great eaters upon you - "Mei ha'Nahar ha'Atzumim" (7)!

Radak: They will rejoice with them if Retzin and Pekach will rule in Yerushalayim. "Mesos" is Samuch to "Es". Similarly, "Mekom Lo Yada Kel" (Iyov 18:21) - "Mekom" is Samuch to "Lo".