It's all to do with the technology and profit. Electricity generation can be quite profitable - so lots of research and technology for the cheaper and easier options than there is for energy storage. The profit for energy storage is pretty much the difference in off peak prices to peak electricity prices. Buy cheap, sell expensive. Not so profitable so the big players haven't invested as much. So far the reliable storage is lithium batteries - a finite resource, but also limited in how quickly they can dig out the lithum. They are developing other battery systems, such as one based on sodium (from sea salt) which is far more abundant and should be cheaper.. but a newer technology that is still developing. Apart from batteries there is hydrogen (hydrogen from water) which can be used in place of gas, a reasonably new industry with a few UK plants operating and a few under construction and in planning. These can create the hydrogen and also be a 'petrol staton' in the same location - you don't need tankers, just a water supply and an electricity power line. But very correct, energy storage is lagging behind electricity generation - once it is balanced then we can move forward with a cheap, renewable electricity generation system that is future proof when the oil runs out and independent on foreign energy sources (such as Russian oil, or african solar farms). A couple of other options like pumped hydro and high pressure air - pump water up to a high reservoir, let ot go down when needed idea - but these schemes are limited to peak supply only - not enough capacity or suitable stores. So batteries - still a developing industry that needs to catch up (and perhaps need some incentives to build the kit).
Ocean power... yup, a bit of a holy grail to get reliable generation from the tides, a lot of systems have been tried and fail with reliability. That would be the best option if it can work, it would give a predictable output every day.. but reliability and maintenance ruins most it. Storms are a big issue - wind turbines can revolve to avoid damage, anything floating on the sea gets hit by everything. Off shore wind turbines are a more established technology onshore and benefit from this offshore. You could do river tidal schemes, the Mersey and the Severn have been looked at but... you would essentially need to put a weir at the end of the river to capture the tidal water at high tide, let it out at low tide, but the environmental types don't like that - the fish get upset.