Magento2- Session Empty After Being Set

I have some code that, when a button is clicked, sets a session value to 1. Then (in the same frontend place) checks that value and if present, do something else.

This is my Controller (skimmed to relevant code):

<?php
    namespace Vendor\Module\Controller\Index;

    class Search extends Action
    {
        const USERBIKE = 'userbike';

        public function execute()
        {
            # other code

            if ($this->getRequest()->getParam(self::USERBIKE)) {
                $block = $this->layoutFactory->create()->createBlock('Vendor\Module\Block\Garage');

                if ($block->getGarageCollection()->getFirstItem()->getCustomerId()) {
                    $block->getCoreSession()->setUserBike(1);
                }

                $writer = new \Zend\Log\Writer\Stream(BP. '/var/log/logfile.log');
                $logger = new \Zend\Log\Logger();
                $logger->addWriter($writer);
                $logger->info(print_r($block->getCoreSession()->getUserBike(), true));
            }

            # other code
        }
    }

Which takes data from this .phtml form:

<?php
    $vendorBlock = $block->getLayout()->createBlock('Vendor\Module\Block\Garage');
    $session = $vendorBlock->getCoreSession();

    $writer = new \Zend\Log\Writer\Stream(BP. '/var/log/logfile2.log');
    $logger = new \Zend\Log\Logger();
    $logger->addWriter($writer);
    $logger->info(print_r($session->getUserBike(), true));
?>  

<div class="amfinder-common-wrapper amfinder-<?php echo $block->escapeHtml($block->getFinder()->getTemplate()); ?> <?php echo $block->getHideClassName() ? 'amfinder-hide' : ''; ?>"
     id="<?php echo 'amfinder_'. (int) $block->getFinder()->getId(); ?>"
     location="<?php echo $block->escapeHtml($block->getLocation()); ?>">

    <form method="post" action="/garage/index/search">
    <!-- etc. -->
        <button class="button action primary"
                name="userbike"
                value="1"
                title="<?php echo $block->escapeHtml(__('Use My Bike Instead')); ?>"
                type="submit">
            <?php echo $block->escapeHtml(__('Use My Bike Instead')); ?>
        </button>
    </form>
</div>

Clicking the button creates logfile.log which shows my value to be 1. However, after the page refreshes, logfile2.log is empty. It seems it works but then doesn't?

My session stuff:

<?php
    namespace Vendor\Module\Block;

    class Garage extends Template
    {
        protected $_coreSession;

        public function __construct(
            # etc.
            \Magento\Framework\Session\SessionManagerInterface $coreSession
        )
        {
            $this->_coreSession = $coreSession;
            # etc.
        }

        public function getCoreSession()
        {
            return $this->_coreSession;
        }
    }

How can I get the session values correctly so that they persist after page refresh? What is wrong with my current code?