I agree with what has been said here. It's crucial to be patient when starting out with new platforms, especially if you're working on a marketplace "bidding" system because the competitiveness is high. Not to mention the fact that these long-term clients may have already picked out their desired writers whom they would love to work for them. The key is building a reputation and ensuring that you are placing your best foot forward at all costs. This will take a long time - but the benefits in the long-run would serve you wondrously.
Additionally, I also agree that you could ask the management or the support team of the platform regarding your bidding. I had encountered an instance wherein I had also struggled with achieving bids at a new(er) platform. That being said, I contacted my referral within the company and asked how I could turn this around. What they had done was provide me with an extensive input on how I interact with clients, how the clients have been used to interact with, and what forms of interactions have reaped the optimal results for everyone in consideration. I had applied this; and a week later, my bidding success rate improved dramatically from nearly just 1 per day to 5-10.
If you trust this system and the company, there's no harm.
Best of luck in your endeavors. I know it can be excruciating at times.