So, we know that the romans were extremely democratic for thier time, even during the imperial period, the elected senate held considerable power. Historical sources tell us that the various conquered people were treated fairly well by the romans. Take the gauls for example, the romans built cities, provided darinage and sanitation, made magnificent aqueducts, and constructed ampitheatres for them, while previously they were nothing but a bunch of tribes living in mud huts and sometimes even commiting human sacrifices, the romans gave them rights and completely accepted them in thier society, even allowing them into thier army, essentially civilising what were previously a savage and unlearned people.
Why then, did the conquered peoples revolt against rome at the first oppurtunity of destroying the empire?Some might say that living as a master in your own house is better than living as a servant in a palace. But in those times the reality for the average person was that they always had to live as a servant, either to some tribal chieftain, or to some far away emperor.
Why then did the people side with thier chieftains, who could only provide shacks and mud houses for them, and not with the romans who provided them with all the comforts of a civilised life. Why indeed, did they fight initially against romans expansion at all, while in the end they were to become citizens after being defeated after all.
It seems you have quite some misconceptions about how the Roman Republic and Empire functioned. I can link to some earlier threads with more accurate information.
Firstly, Rome was not "extremely democratic" for its time. As mentioned here by u/LegalAction and here by u/toldinstone, the Roman Republic was a "mixed constitution" and its leaders had a rather negative view of the more democratic systems of Athens and some other Greek states. The Roman senate was not directly elected; it was in fact an advisory council of former magistrates, and in elections for magistrates one had to physically be in Rome, and the citizenry was also divided into voting classes with the wealthy having far more influence. This you can read about in these two older threads, both written by u/Celebreth, and u/bigfridge224 has written about how senators were elected here.
While Roman construction projects in the provinces could be beneficial for the population, Roman conquest was very brutal, with the sacking of cities and enslavement of the surviving population being common. This, with Carthage as example, has u/Iguana_on_a_stick written of here and u/MichaelJTaylorPhD in this answer.
My computer is almost running out of battery: later I shall add more links explaining Roman imperialism and subject peoples