Russia wants a navy base. Period. It’s not a mystery. If you understand that Putin is supporting Assad for the purpose of having a navy base with a harbor that doesn’t freeze in the winter, and that is not cut off from the rest of the world by straights guarded by NATO, then Russia’s behavior becomes totally predictable and understandable.
How do I know this? Easy. Putin said as much. In 2008 if my memory does not fail me, he announced plans for a new oceanic fleet by 2020, with navy bases in Libya, Syria, Yemen, and Venezuela. Then came the Arab Spring and wiped away Kadaffi in Libya, and created civil wars in Syria and Yemen.
Russia already had a small base in Syria that seemed about to be lost, just like Sevastopol in Crimea would be lost when the treaty with Ukraine expired. Which is why Putin installed his man as president, but he was ousted in an uprising in 2014. So Putin invaded Crimea in order to hold on to Sevastopol. After that victory he turned to Syria and decided to hold on to that base as well, which is why he has backed Assad for a year now. Another stop gap measure has been a cooperation with Iran, using one of their bases in the Indian Ocean.
Libya and Yemen are out of reach now, but Venezuela is un unknown case. The area where the base presumably would be built has been closed off for civilians, and there are a lot of work going on under foreign direction. Not Russian though, but Asian. Tensions have gone high recently when foreign work leaders have pushed local crews beyond what they deem acceptable.