Don’t know what “expensive stuff” you’ve used but you’re almost certainly using the wrong product; additionally you’ll have problems if there is excessive movement between the bath & the tiles, no forced or natural ventilation in the bathroom or, no offence meant, you never clean it down; or perhaps all of the above!
If you use a good quality, low modulus, sanitary grade silicone & follow some simple rules, the bead should stay in place & last for several years before it needs re-sealing; stick on PVC beading around the bath (or anywhere for that matter!) will always look cack & will also be a breeding ground for far more mould spores & other nasties than a decent silicone bead.