Why does my flower count increase. Just started after reaching level 1725?

Oh, sorry, I misunderstood your question. If you are at level 1725, you have hit the maximum level at this time, so the flowers will add up instead of count down. When the next volume is released, a new maximum level will be set, so that all the flowers you have accumulated will count toward that new volume. That's not saying you'll be able to play all the new scenes, as scenes will still be released one chapter per week (5 hidden object scenes and 1 adventure scene) but you will not need to place flowers on your island to progress. If you want to control how fast you level up, you can place decoration in storage and place them on the island(s) only when you want to level up.

You must have sold some decoration or put some in storage. When you do either, flower value is removed from your island, such that the number of flowers you need to reach the next level is greater.

The number of flowers you need will go down when you move decoration from storage back to your island, or when you buy more decoration. When you buy decoration, the flower value will count after construction is complete and you remove the red ribbon. You also earn flowers by renovating your landmark, sending Jack on certain deliveries, and prizes from events and competitions. Once the number of flowers needed reaches 0, you will level up, and the game will display how many flowers you need to reach the next level. Flowers needed for an individual level will typically be between 90 and 495.