Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
A Muslim must believe that Allah, the Most High, is Wise in His creation and in His commands, and that all His actions are based on wisdom, justice, and mercy, whether a servant understands the wisdom behind them or not. Allah, the Most High, says:
“He is not questioned about what He does, but they will be questioned.” [Al-Anbiya: 23]
Allah, Glorified and Exalted is He, has informed us about Hellfire and the punishment of the Hereafter so that we may beware of it and protect ourselves from it by obeying Allah—not so that we become preoccupied with asking why Hellfire was chosen rather than something else. Allah, the Most High, says:
“And fear the Fire which has been prepared for the disbelievers.” [Aal 'Imran: 131]
Furthermore, the question is based on an inaccurate conception. The punishment of the Hereafter is not limited to Hellfire alone; rather, it includes both physical and spiritual forms of punishment.
Among the greatest forms of spiritual punishment is that the disbelievers will be deprived of seeing Allah, the Most High. Allah says:
“No! Indeed, they will be veiled from their Lord on that Day.” [Al-Mutaffifin: 15]
They will also be deprived of Allah's merciful regard toward them and of His honoring them. They will hear rebuke and threats, and they will be deprived of the companionship of the prophets, the truthful, and the righteous.
As for physical punishment, it includes Hellfire, as well as the bitter cold, chains and shackles, iron clubs, boiling water, and the food of Zaqqum, along with other forms of punishment that Allah, the Most High, has informed us about.
Allah, the Most High, says:
“And for them are hooked rods of iron.” [Al-Hajj: 21]
And He says:
“When the shackles are around their necks and the chains, they will be dragged * in boiling water, then in the Fire they will be burned.” [Ghafir: 71–72]
And He says:
“They will surely eat from the tree of Zaqqum, * filling their bellies with it, * then drinking boiling water over it.” [Al-Waqi'ah: 52–54]
Therefore, Hellfire is not the only form of punishment in the Hereafter. Rather, it is the greatest and most prominent abode of punishment. Allah, the Most High, has combined for its inhabitants many different forms of physical and spiritual punishment, and all of this is in accordance with His perfect wisdom and justice.
The Muslim is required to submit to the information given by Allah, fear His punishment, and strive to be saved from it through faith, repentance, and righteous deeds, rather than becoming preoccupied with matters that do not lead to any action.
And Allah, the Most High, knows best.