There are multiple reasons for actors to turn producers
Firstly the bigger stars become producers to take control over the whole filmmaking process, earn majority share of the profits and keep the IP rights of the film for the future. This ensure that they can make their kind of films and earn handsome profits. Almost all the big stars have produced their own films not equally successful but it means that even if they are not successful they still have their Star Power to work outside their production and make up for the losses. SRK, Aamir, Akshay, Ajay, Salman, Amitabh, Jeetendra, Dharmendra among others and actresses like Hema Malini, Priyanka Chopra, Anushka Sharma, Alia Bhatt, Kriti Senon, Tapsee Pannu etc turned producers.
Secondly, many actors turn producer to give themselves credibility by associating with meaningful cinema. There have been actors who may not have done anything substantial in terms of acting but then producing award winning films enhance their credibility and allow makers to give them more serious roles. John Abraham for example was largely considered a non actor till.he produced National Award winning films like Vicky Donor (won him a National Award) leading to collaboration with Shoojit Sircar as an actor in another National Award winning films Madras Cafe. Actress Rimi Sen who is nowhere to be seen now out of sudden produced a National Award winning film Budhia Singh: Born to Run.
Thirdly, actors who either have been typecast in a particular type of role or who wanted to project themselves as bigger stars tend to produce films that they want to work in. Even Ranveer Singh after series of failures put in his own money to showcase himself with Dhurandhar which paid rich dividend to him. Nana Patekar put in his money in making of Ankush, a film that made him a star. But this can be a double edged sword. Rajpal Yadav lost all his savings trying to make a film with him in lead role. Mithun Chakraborty had earlier lost huge money trying to project himself as an A lister with Boxer that flopped. Abhay Deol lost his money and had to sell his flat in making One by Two.
There are some actors who fail badly and decide to produce films to have another avenue of income particularly if they have support from close friends and family. We have Arbaaz Khan producing Dabangg and making millions out of it courtesy the stardom of Salman Khan and he bflllowed it with Dabangg 2 but his other films were not as lucky. Earlier Sohail Khan also milked Salman’s stardom with films like Hello Brother, Auzaar, Maine Pyar kyon kiya, Partner, Ready, Jai Ho etc. Salman also helped his son, a once upon a time actor Atul Agnihotri, who was the producer of Bodyguard. Another flop actor Nikhil Dwivedi who flopped in films like My Name is Anthony Gonsalves and Tamanchey etc eventually turned full time producer with films like Veere di Wedding, Dabangg 3, and recent film Bandar.
Lastly we have out of work actors who are not getting roles who decide to produce films to stage a comeback or remain relevant. Amisha Patel tried to produce a film Desi Magic which got stuck and is still unreleased due to lack of finances. Preity Zinta after years of absence from the silver screen decided to produce a film called Ishq in Paris, which unfortunately failed miserably.