I'll tell you you why, but it requires a little bit of history.
1. The Syrians state acquired the Golan from the French in 1944. They used it as a staging area to attack Israel from 1948 on.
2. They used it to attack Israel in the 1967 war.
3. They lost it in battle to Israel in 1967.
4. Israel controlled it from 1967 until 1981. They legally annexed the Golan by vote of the Knesset in 1981. It then became a part of Israel.
5. The Syrians had the territory for 19 years in total. Israel has had it for almost 50 years now. The Syrians lost it in battle. This is a time-honored way in which territory is changed.
6. The Syrian claim to the Golan is the same as Muslim claims to all non-Muslim land. They think it should belong to them.
7. Should Spain return itself to the Muslims? The Muslims conquered it in 711 and ruled it for almost 8 centuries. The Spanish finally kicked them out in 1492. I hear no clamor for Spain to return itself to Muslim rule.
8. Golan is now part of Israel.
This.
Golan was part of the sovereign state of Syria.
Israel laid no claim to it... during the 1967 war Israel occupies it. That’s the status. It is occupied Syrian territory. Dejure Syrian, defacto Israeli occupied. No other country recognizes the Golan as Israeli territory.
There may be hundreds of good reasons why Israel won’t give back the Golan. But the Syrian President sould be the least person you’d expect simply to forfeit his country’s claim.