Can someone explain to me why the market is going up like a rocket?

Probably not. Some possibilities:

Greed.

FOMO.

Animal spirits

It was down like a submarine in March. It's "only" up 4% YTD.

Risk-on with Trump -- he seems, to me, to measure and change his actions to please the stock market

Inflation is up. Stocks are relatively better than cash at those times.

forward earnings yield > treasury yield and that typically improves with growth/time.

AI buildout is good for the economy. Lots of CapEx with expectations for returns on invested capital. Stimulus now -- could bite some in the future.

Lots of recent deregulation is good economic stimulus.

AI might deliver big productivity gains, do you want to sit them out in cash?

Big tech is rebounding after a recent dip.

Govt spending is up -- there is zero austerity so far from Trump. Good now but pain eventually.

Tax stimulus coming from the Big B Bill.

War is a stimulant for the economy unfortunately and there are several going on and maybe more to come.

Europe is raising defense spending significantly now that US has threatened to abandon them and/or asking them to pay their "fair" share.

Fed buying tons of short term t-bills to keep things liquid and flowy

So much extra money to be invested from all over the world as upper middle class populace booms

Timing the market is hard, time in the market is easy -- except for 10-30 months every 10-30 years.

Even Berkshire is buying back their shares.

But I didn't convince myself let alone think that that should convince you.