Why are buttons added one after another in the multi-level menu of the Telegram inline bot (telebot)?

Question

Python

Multilevel menu:

@bot.message_handler(content_types=["text"])
def any_msg(message):
    keyboardmain = types.InlineKeyboardMarkup(row_width=2)
    first_button = types.InlineKeyboardButton(text="1button", callback_data="first")
    second_button = types.InlineKeyboardButton(text="2button", callback_data="second")
    keyboardmain.add(first_button, second_button)
    bot.send_message(message.chat.id, "testing kb", reply_markup=keyboardmain)

@bot.callback_query_handler(func=lambda call:True)
def callback_inline(call):
    if call.data == "mainmenu":

        keyboardmain = types.InlineKeyboardMarkup(row_width=2)
        first_button = types.InlineKeyboardButton(text="1button", callback_data="first")
        second_button = types.InlineKeyboardButton(text="2button", callback_data="second")
        keyboardmain.add(first_button, second_button)
        bot.edit_message_text(chat_id=call.message.chat.id,message_id=call.message.message_id, text="menu",reply_markup=keyboardmain)

    if call.data == "first":
        keyboard = types.InlineKeyboardMarkup()
        rele1 = types.InlineKeyboardButton(text="1t", callback_data="1")
        rele2 = types.InlineKeyboardButton(text="2t", callback_data="2")
        rele3 = types.InlineKeyboardButton(text="3t", callback_data="3")
        backbutton = types.InlineKeyboardButton(text="back", callback_data="mainmenu")
        keyboard.add(rele1, rele2, rele3, backbutton)
        bot.edit_message_text(chat_id=call.message.chat.id,message_id=call.message.message_id, text="replaced text",reply_markup=keyboard)

    elif call.data == "second":
        keyboard = types.InlineKeyboardMarkup()
        rele1 = types.InlineKeyboardButton(text="another layer", callback_data="gg")
        backbutton = types.InlineKeyboardButton(text="back", callback_data="mainmenu")
        keyboard.add(rele1,backbutton)
        bot.edit_message_text(chat_id=call.message.chat.id,message_id=call.message.message_id, text="replaced text",reply_markup=keyboard)

    elif call.data == "1" or call.data == "2" or call.data == "3":
        bot.answer_callback_query(callback_query_id=call.id, show_alert=True, text="alert")
        keyboard3 = types.InlineKeyboardMarkup()
        button = types.InlineKeyboardButton(text="lastlayer", callback_data="ll")
        keyboard3.add(button)
        bot.edit_message_text(chat_id=call.message.chat.id,message_id=call.message.message_id, text="last layer",reply_markup=keyboard3)

When moving to the inner layers of the menu, the buttons of the previous layers are not removed, and when returning back, buttons are added down one after another.
I took the code from the video on youtube , everything works as intended for the author of the video, but my buttons line up one after another, how can I fix this?