Why do you think that only the Senate has the power to hold impeachment trials?

Division of powers. The House (supposedly representative of the population at large) has power over money. Appropriations bills MUST originate in the House.

The Senate has power over more 'elitist' things like approving presidential appointments. That's just kind of the mindset the founding fathers had ... rough and tumble politics were supposed to be representative ... therefore in the House, and deliberative, less political, more 'learned' debate items were supposed to be in the Senate.

These United States are a republic. There was, and still is, a concern about states with large populations exerting too much control over states with less. Giving the Senate the power to try impeachments makes it in theory be an equal vote of the States rather than controlled by a few large states.

Read it in the constitution.