Paying teachers who teach Torah is a relatively new phenomena. TB Bekhorot 29

Daf TB Bekhorot 29 lists mitzvot one is not allowed to accept payment for. Surprisingly one is teaching Torah. “This halakha is also taught in a baraita: “Behold, I have taught you statutes and ordinances, as the Lord my God commanded me” (Deuteronomy 4:5). Just as I learned from God for free, so too, you learned from me for free. And from where is it derived that if one cannot find someone to teach him for free that he should learn even by giving payment? The verse states: ‘Buy the truth, and do not sell it; also wisdom, and instruction, and understanding” (Proverbs 23:23). And from where is it derived that one should not say: Just as I learned by giving payment, so too, I will teach it by receiving payment? The verse states: ‘Buy the truth, and do not sell it.’” Sefaria.org translation)

“The Rambam (פרק ג' מהל' תלמוד תורה הלכה י') rules that it is forbidden to involve oneself in Torah alone and survive on Tzeddakah, and not do any other work which will enable him to earn a living, and to do this is in fact a Chillul Hashem, and a disgrace to the Torah, because it is prohibited for one to derive benefit from the words of Torah in this world; he then cites some of the sources presented above to back up this view that one must have a means of support for himself other than Torah.  The Rambam reiterates this position, albeit in brief, in his Peirush HaMishnayos in Nedarim (פרק ג' משנה ד'), and he rules this way as well elsewhere in his Mishneh Torah (פרק י' מהל' מתנות עניים הלכה י"ח), saying that even a great Talmid Chochom must engage, if necessary, in even a disgusting type of work rather than accept money from others, and he cites examples of Gedolei Yisrael who had menial jobs and refused to accept money offered to them by other people.  This position is also quoted by the Tur (יורה דעה סימן רמ"ו); in the Shulchan Aruch, the Ramo (שם סעיף כ"א) writes that one should not plan to become wealthy by being involved in Torah, because one who thinks that he will, will not achieve the crown of Torah, and then he too quotes the position cited by the Rambam (שם) and by the Tur (שם) prohibiting one to derive personal benefit from the Torah.” (Rabbi Michael Taubes, https://www.koltorah.org/articles/receiving-payment-for-teaching-torah-by-rabbi-michael-taubes)

Over time, practical economic realities made full-time unpaid Torah scholarship impossible, leading to widely accepted exceptions.

The Chasam Sofer too (שו"ת חתם סופר חלק חושן משפט סימן קס"ד) writes that because the Torah will be lost unless people will get paid to be involved in its study, it is permissible today to derive personal benefit from the Torah, and he says as well that the community must hire someone whose job it is to be available for Torah guidance.  Rav Moshe Feinstein (שו"ת אגרות משה יו"ד חלק ב' סימן קט"ז) agrees to this position as well, and encourages people to accept whatever rewards are necessary in order to continue to grow and develop in terms of Torah.  A full analysis of this subject, including a description of many of the sources cited above, is presented in the Sefer Shaarei Talmud Torah (שער ו' פרק ג'), while a brief synopsis is presented by the Mishnah Berurah, in his Biur Halacha (אורח חיים סימן רל"א בד"ה בכל), who notes that under certain conditions, even the Rambam would agree that one may get paid for one's involvement in Torah. (Rabbi Michael Taubes, https://www.koltorah.org/articles/receiving-payment-for-teaching-torah-by-rabbi-michael-taubes)

Here are some other rationalizations why teachers deserve to get paid today.

Compensation for Time (Sechar Batalah): Teachers are technically paid not for the sacred knowledge itself, but as compensation for lost working time or wages they could have earned elsewhere.

Childcare and Supervision: Payment for teaching young children is permitted because it includes watching, disciplining, and caring for the students rather than just pure instruction.

Written vs. Oral Law: Some authorities distinguished between the Written Torah (Mikra) and the Oral Law (Gemara/Talmud), though standard communal practice evolved to support rabbis and educators through full-time stipends.

Communal Need: Later authorities—such as Rabbi Yosef Karo (Kessef Mishneh)—ruled that setting aside the rule is permissible under the principle of Eis la'asos la-Shem (it is a time to act for God to keep Torah from being forgotten)