Here is one of the many posts I have made regarding Saruman. It illustrates a huge possibility because originally he was very dedicated to his charge.
Here a few of my responses that should readily explain the possible reasons for Saruman.
Morgoth was more of his leader and dark mentor than master. Aulë was Sauron and Saruman's master Vala, hence why both Saruman and Sauron share the affinity and skill to create, craft, and build. Sauron was Morgoth's lieutenant, they didn't, in fact, even align ideologically. Morgoth's base desire was to destroy and recreate the world as his own, hence his seeking the Flame Imperishable. Sauron desired subjugation and dominion. He didn't care of you had your own opinions and etc as long as you served him. Sauron saw the ability to pursuit his craft untethered by serving Melkor, whom of course poured much of his power into developing the feel creatures of the world, dragons, orcs, etc.
If you want to get even more into it Sauron and Saruman are more involved than most realize being that they are both Maia under the Vala Aulë, who was known as the craftsman Vala. Aulë created the dwarven rave, which is why they are lesser than men, elves, and hobbits. In fact Erü Illúvatar almost destroyed the dwarves after he caught Aulë, but pitied him and understood his inherent desire to create without a malicious intent. So he spared the dwarves, only allowing them to awaken after the elves and men. Now Sauron and Saruman answered to their master, Aulë, this is a reason why Sauron and Saruman both are greatly skilled in crafting and creating because of whom they originally served. Sauron followed Melkor/Morgoth in order to craft without the hand of the Valar intervening, plus he saw the opportunity to further his own desires after Morgoth's seduced him to the "dark side". Sauron also begged forercy a few times, claimed to be reformed, lied, cheated, then helped secure the demise of the Numenoreans, and yada yada. He's a badass but a huge twat when necessary to not get his butt kicked by daddy.
Which also leads to an interesting parallel. Sauron followed Melkor mainly in an effort to further his own agenda. He saw him as a "go-getter", in a way, and understood by following him that he would be able to tinker, and create without the scrutiny and rules of The Valar. It could be interesting to see how Saruman saw working with Sauron as a similar relationship. Though Saruman sought to acquire the ring himself (I'm really generalizing and oversimplifying) he probably saw the same desire to create, and control, and tinker much like Sauron and thus followed the more powerful " go-getter" as a means to an end. Plus it's a running theme with Aulë and his subordinates. Aulë created the dwarves, whom were only spared because Erü empathized with Aulë and his apology (again, huge simplification), so Sauron seeing Morgoth create Orcs (however he did it, since it's a heated debate), and many other fell beings, would reasonably be similar to how Saruman saw Sauron's creations and endeavors as an inspiration to also see such freedom to create and dominate. Again HUUUGGGEEEE oversimplification of many of the relationships and history, but still enough to form an interesting conjecture. Also I'm on mobile, so I apologize for any errors.
These were replies to different comment threads so they don't flow completely. (Granted some of my info is a bit generalized)
Edit: Also this is just a look at why Saruman may have been seduced. It is apparent as well that he was jealous of Gandalf (in a few ways), in fact if memory serves he was nominated to be the leader of the Order originally (or maybe it was the White Council, I need to check) over Saruman, but Gandalf said "Nah man, that ain't me."