If time travel were possible, whether forward or backward, there would likely be various reasons why not everyone would own a time machine:
Technological limitations: Time travel, especially in a practical and controllable manner, would likely require extremely advanced and complex technology. It may not be feasible for every individual to possess or operate such technology due to its complexity, cost, or resource requirements.
Regulatory restrictions: Time travel could have significant implications for altering history, causing paradoxes, or disrupting the fabric of spacetime. Governments or regulatory bodies may impose strict controls on time travel technology to prevent misuse, maintain stability, and avoid catastrophic consequences.
Ethical considerations: Time travel raises numerous ethical dilemmas. Altering past events or interfering with the course of history could have unforeseen consequences and raise questions of moral responsibility. There may be ethical guidelines or restrictions on the use of time travel to prevent harmful or unethical actions.
Potential dangers and risks: Time travel could introduce a range of dangers and risks, such as unintended changes to the timeline, paradoxes, or the possibility of getting trapped in a different time period. Not everyone may be willing to take on the potential risks and uncertainties associated with time travel.
Limited access or availability: Even if time travel were possible, it might be limited to specific organizations, institutions, or highly specialized individuals. Access to time travel technology could be restricted due to its scarcity, strategic importance, or concerns about maintaining control and preventing misuse.
Temporal stability and preservation: It is conceivable that time travel could pose a threat to the stability of the spacetime continuum or disrupt the natural flow of time. Limiting the number of time machines and their usage could be a precautionary measure to maintain the integrity of the timeline and preserve the natural progression of events.
These are hypothetical considerations based on the assumption that time travel is possible. It's important to note that time travel remains purely speculative at present, and no scientific evidence supports its existence.